Akademik

худо будет
ХУДО <ПЛОХО> БУДЕТ (кому) coll
[VP; impers; these forms only; usu. a clause in a compound sent; preceded by one or more clauses expressing prohibition, warning etc; often after а то, не то, иначе etc]
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(if s.o. disobeys an order, fails to do what he should do etc) there will be trouble (for him and/ or another or others):
- X-y худо будет{{}} X will be sorry;
- X will be in hot water;
- X will have the devil to pay;
- X will come to a bad end;
- [when the situation is already bad] things will only get worse.
     ♦ "Раз подъехал к нему и говорю шутейно [substand = шутливо]: "Пора бы привалом стать, ваше благородие - товарищ Мелехов!" Ворохнул [substand, here = сверкнул] он на меня глазами, говорит: "Ты мне эти шутки брось, а то плохо будет" (Шолохов 5). "One day I rides up to him and says joking like, Time to call a halt, Your Honour-Comrade Melekhov!' And you should have seen his eyes flash! 'Just you drop those jokes of yours, or you'll come to a bad end,' he says" (5a).

Большой русско-английский фразеологический словарь. — М.: ACT-ПРЕСС КНИГА. . 2004.