Quoting: nauczyciel
and when you wish someone "good luck" on an exam, they say "no thanks"then you say "bad luck" and they say "thanks"
actually the usual answer to "powodzenia" is rather "nie dziêkujê" = "I don't thank you"
("no, thanks" = "nie, dziêkujê" with comma) - I'm not 100% sure about it, but that's my impression (and I had many exams in my life)
and you don't say normally "bad luck", but wish them something appareantly unlucky specifically for the situation (breaking a pen/pencil - before an exam, breaking the legs - before a run)