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ПАЛЬЦА (ПАЛЕЦ) В POT HE КЛАДИ кому coll VPimper these forms only fixed WO

s o. should be dealt with very carefully (because he is cunning, quick to take advantage of another's negligence or gullibility, cannot be trusted etc)

X-y пальца в рот не клади - you have to be on your guard with X

X is not someone to mess around (to trifle, to fool) with X is not (a man (a woman)) to be trifled (messed) with you can't (I wouldn't etc) trust X an inch.

Меньшевикам очень хотелось к столу, но винтовки бросать не хотелось. Хозяина-то они не боялись, но уже поняли, что дяде Сандро пальца в рот не клади (Искандер 3). The Men-sheviks very much wanted to sit down at the table but did not want to let go of their rifles. Although they were not afraid of the owner, they realized that Uncle Sandro was not to be trifled with (3a).

«Что вы скажете насчет Сноудена?» - «Я скажу вам откровенно, -отвечала панама, - Сноудену пальца в рот не клади» (Ильф и Петров 2). "...What do you think of Snowden?" "I tell you straight," replied the Panama, "I wouldn't trust him an inch" (2a).