I can't say, i haven't had my work ripped off before. Though if someone did, i would first be honored that they thought my work was good enough to the point where they ripped. lol Then i'd confront them.
I'd be happy that someone likes my work so much although I would ask to credit me instead of themselves and if they didn't take further action if I felt it was necessary.
I would be both honored and disappointed, I would be honored because someone actually liked my work enough to rip it, I would be disappointed because it would mean they are not good enough to create there own work and they rip it so people think they are good with graphics. But it has never happened to me...yet