I just caught my friend jacking off to a pic of my sister while in the same bed as me

This deserves some context. So my friends like to tease me about having a hot sister and she posted a picture if herself in a bikini on insta, so every once in a while that gets brought up. So our school went on a trip to D.C. and we get a hotel and there are four guys amd two beds in each room. So me and my roomies are in the room watching tv and all the sudden the guy next to me says he wishes it was my sister in the bed with him. We laugh, but then the guy pulls out the picture and he says I’m really horny. He then goes under the covers and I start seeing a lot of movement. He says, don’t open the covers I am jacking off. Me, assuming he is joking, pulls off the covers and low and behold, he has his dick in one hand and the pic in the other. I yelled what the fuck and he put his dick back in his pants. I asked him what hell and he said it was just a joke and that he wasn’t actually going finish. I said it didn’t matter. After yelling at him a little bit we all calm back down. But this man had the nerve to say he was still horny. He wouldn’t shut up about it so we said he could go in the shower and jack off. He came back thirty minutes later and we sat in awkward silence until we went to bed tl;dr guy joked about jacking off to my sister right next to then actually did it, then went in the shower and jacked off. I could not make this shit up if I tried.