"Вдруг бывает только пук" (suddenly happens only fart) is a colloquial humorous phrase, which is a retort to a person asking "а вдруг?" (what if?). I can't find etymology of this phrase. Where did it come from?
1 Answer
With Russian being my native language, I came across this phrase only a few times. This, I believe, is an example of typical Russian street-made-up expressions. Answering that to "А вдруг?" would not be very polite, by the way.