What would you do if you caught your brother masturbating into your thongs/ gstrings (hes 16 im 14)?

I caught him in his room on his bed with nothing but my blavk and purple thong on, he was masturbating and didn't stop even though he saw me, i think he's been doing this for a while as im still missing 4 pairs of pant's. and some tights and a bra. what should i do