"That's a bad one", loosely. Or "you put a bad (one)" more literally. The word order is also reversed, and the correct form would be "sinä pistit pahan". But "pistää" ("pistit" is a second person imperfect) can also mean "to stab", and I yesterday I was stalking all the Farmakon-guys from a so close range that I had to restrain my stalker-nature not to stab them with joy.
It's actually quite scary that some crazy Italian suddenly throws in Finnish language without warning. And so is this thing how I'm playing a teacher.