Depending on who the guy was I would either run for the hills or I would join him.
Are we talking about using your panties to masturbate, as in rubbing them on his penis as he does it, or is he actually wearing your underwear as he masturbates?
not ask for them back.
give me an answer for both
Assuming he is jacking off with rubbing the panties on his cock, I would wait until he cums and shove the panties in his mouth and then blow him.
OK. If he's masturbating by using your panties to rub against himself, then he probably just likes the feel of them. In the very least, you should make him buy you some new ones. But if you really want to get something out of the situation, find out which panties of yours really turn him on, and think about some ways to integrate them into your sex life. You don't want the panties to be the object of his desire, obviously, but they probably do turn him on. You might be surprised at how much more into it he gets when you tease him with your panties before you have sex.
On the other hand, if he's actually wearing your panties as he masturbates, then you might need to be a little more open minded about the situation--because no matter what he tells you, he wants to wear panties more often than just when he pleasures himself. I say you should give him an ultimatum, he wears panties all of the time or not at all.
If he decides not to wear them, and you catch him doing it again, ditch him, because not only can't he be trusted, he doesn't trust you enough to tell you what he really wants.
If he decides to commit to wearing panties though, then you two have a little secret that you can have some fun with (as long as you can deal with having a boyfriend who wears women's underwear).