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It reminds me of the usage of jinx, and old word which (at least in my experience) recently becoming much more popular amongst young people:

to foredoom to failure or misfortune : bring bad luck to

_{(source: Merriam Webster)}

"Don't jinx it" is a reasonably commonly heard phrase nowadays.

The answer by Glorfindel identifies "jinx" as a very good option, which I agree with for the "superstition" meaning; it seems to substitute well in the form "jinx it", such as "I don't want to jinx it". However, I don't think it's appropriate for more material concerns over what you call "mental poise".

The most appropriate word I can think of for that meaning is "choke", using the intransitive verb definition 4 from here:

to lose one's composure and fail to perform effectively in a critical situation

Alternatively, if you really need a single word or phrase that mixes superstition with mental poise, the closest I can think of is "psych out" with usage something like "I don't want to psych myself out." It can be used to express this kind of sentiment: "I don't want to worry about a superstition because doing so would upset my mental poise and cause me to fail." This is somewhat tenuous and it would be clearer if you specifically mentioned superstition as well, but I don't know of anything closer.

To reiterate, I don't think a single phrase perfectly aligns, but these each can apply to some of the situations:

• If you want to avoid a superstition, "I don't want to jinx it."


• If you want to preserve your mental poise, "I don't want to choke."


• If you want to preserve your mental poise by avoiding a superstition, "I don't want to psych myself out thinking about it." (With "it" being the superstition.)

"queer the deal" has a very specific, clear, meaning, crossing over between "superstition" and "mental poise".

No, it doesn't mean that. If that is a quote from somewhere, please provide the source of the quote.

To "queer the deal" does not mean to jinx something.

Queering the deal means to have some (usually last minute) new condition or circumstance to contend with, which threatens the delicate balance of (a perhaps not altogether above-board) negotiated arrangement. Last minute demands of facilitators who want to increase their cut of the deal are typical examples. The ability to queer a deal is the essence of pork barrel politics. The phrase was established by 1900.

"A good cigar," said the dealer "you can have it now if you want it." The coachman was wrath his employer purchased a horse, he said he had always gotten a rake off of $25 from the dealer and he now demanded $75 as his commission for inducing his employer to buy an automobile. If money wasn't forthcoming he he would queer the deal.

The Horseless Age: The Automobile Trade Magazine, Volume 8, 1901.

So the alternatives should preserve this sense of meddlesomeness.

The first that comes to mind is "scotch the deal", but I rather think this doesn't solve the problem so much as impune the Scots. However it is surviving in the news just fine, at least in British news. Scotch the deal generally implies somebody benefits from the deal not happening at all, while queer the deal is normally used where all parties need some sort of deal to go through to benefit.

"Stymie the deal" is close and has some currency.

In handing down his ruling, federal judge Richard Leon said the Justice Department -- whose antitrust chief, Makan Delrahim, brought the rare case -- failed to provide sufficient proof that the deal would harm competition or consumers. He also warned the U.S. government against bringing an appeal if the purpose was to try to stymie the deal, though the DOJ has not indicated its next steps.

AT&T-Time Warner merger approved, setting stage for more consolidation, Daily Herald, 6/13/2018. https://www.dailyherald.com/business/20180612/att-time-warner-merger-approved-setting-stage-for-more-consolidation

"Muddle the deal" seems like a good option.

While the Reynolds-Lorillard deal shakes up the lucrative but slowing U.S. market, it doesn't alter the global picture dramatically. That makes it unlikely Philip Morris, the global leader in cigarette sales excluding China, or Japan Tobacco, would feel the need to swoop in and try to muddle the deal with any counteroffer, industry watchers said.

Amid U.S. Tobacco Merger, Is the Global Deal Making Done?, The Wall Street Journal,Jul 15, 2014. https://blogs.wsj.com/moneybeat/2014/07/15/amid-u-s-tobacco-merger-is-the-global-deal-making-done/

It sounds like you want to use classical meaning of "queer" not because it is the most "Simple English correct" term, but to add color and dimension to your language. Any of a huge variety of slang terms for "breaking it" will suffice.

Don't scotch the deal

Don't flub the deal

Don't zorch the deal

Don't botch the deal

Really, that list is pretty endless.

You can also throw a little "Darmok & Jilad at Tenagra" (or more precisely, "Shaka, when the walls fell") in there, by adapting a cultural reference- someone who "snatched defeat from the jaws of victory", facepalmed, or let loose lips sink ships. That's trickier, and subject to context. "don't Kee Bird the deal" would play among airplane restorationists.

It is related to the panoply of expressions for which queer is used, comprising various markers - often derogatory, some of them such as the association with homosexuality now considered offensive. Another is the British expression queer street, slang for bankruptcy. (A bankrupt person or business is said to be "in queer street".)

As well as noun and adjectival senses of queer,however, two verb senses have entries in the OED. The first is derived from inquire or query and has no relevance here.

However the second, especially sense 2b is exactly relevant to this question.

b. to queer the pitch: (originally) to interfere with or spoil the
business of a street vendor or performer (cf. pitch n.2 17a); (later
more generally) to interfere with or spoil the business in hand;
similarly to queer a person's pitch. Also in similar phrases, as to
queer the game, to queer the deal, etc.

1846 ‘Lord Chief Baron’ Swell's Night Guide (new ed.) 47 Rule
iv... Nanty coming it on a pall, or wid cracking to queer a pitch.
1866 M. Mackintosh Stage Reminisc. vii. 93 The smoke and fumes of
‘blue fire’ which had been used to illuminate the fight came up
through the chinks of the stage, fit to choke a dozen Macbeths,
and—pardon the little bit of professional slang—poor Jamie's ‘pitch’
was ‘queered’ with a vengeance. 1875 T. Frost Circus Life xvi. 278

The spot they select for their performance is their ‘pitch’, and any
interruption of their feats, such as an accident, or the interference
of a policeman, is said to ‘queer the pitch’. 1889 E. Sampson Tales
of Fancy 38 They could not understand it when their pitch was
queered, and one or two of the gang arrested. 1901 Windsor Mag. Dec.
204/1 I think you and I between us have queered the game. 1912

Chambers's Jrnl. Dec. 795/2 All branches of the administration work
sensibly and effectively so long as you do not ‘queer the pitch’ by
creating exceptions. 1973 E. Lemarchand Let or Hindrance iv. 31

He's a decent lad... He would never have risked queering Wendy's pitch
with Eddy. 1993 Chicago Tribune 19 June i. 14/2 This
presumes..that Nolan doesn't queer the deal by holding more press
conferences to warn how crime-ridden Chicago will become. 2006 Econ.
Times (India) (Nexis) 4 Oct. What queers the pitch for the airlines
is the additional capacity entering the domestic market over the next
three

As a bonafide queer person myself, I've never even heard this particular turn of phrase.

I would either use jinx, as Glorfindel suggests, or potentially curse or hex as all of those terms explicitly evoke the superstitious nature that you were looking for. I do think jinx is the most common, however.

Examples:

Mom: Oh, you're done with your degree, congratulations!

Me: Don't say that yet, you'll curse me!

In my case, I was fully aware that odds were very good that I would graduate (and I did!), but the illogical part of my brain was convinced that if anyone congratulated me on it, I would fail.

The Jewish or Yiddish word "Kinehora" might work. To my untutored ear it sounds like "KAN - UH - HARA." I hear Americans including my wife's Jewish family say it. It means don't jinx it by anticipating it before it's completed.

For example, " Five years and my Ph.D. is almost complete, only weeks to go!" Or celebrating an offer of work or a deal before the contract is signed. People then say, "Don't put a kinehora on it."

Here's a reference: http://www.jewishanswers.org/ask-the-rabbi-category/miscellaneous/?p=1855

Don't sour the deal

One of the definitions at [oxforddictionaries.com] (https://en.oxforddictionaries.com/definition/sour) is:

(verb) Make or become unpleasant, acrimonious, or difficult.

  [with object] ‘a dispute soured relations between the two countries’

As I'm not superstitious, I can't comment on that meaning.

I'm flattered by OP's suggestion that only younger people today use "queer" as homosexual. I'm retired and have always understood it that way. Perhaps it's BrE that's only recently entered AmE.

The 'deal' could be considered a complicated and multi-faceted operation. For this, I would offer,

Don't throw a wrench in the works.

This instills vivid metaphoric imagery of halting the machinations of a complex transaction or process through one's actions or inactions.