At one of the many graduation parties we had, one was in the school uniform. I wore my skirt shorter than normal, and I didn't wear shorts underneath. Only my thong covered my ass and pussy. We were in line waiting to get in and I was hugging my boyfriend from behind. By that time we had already had enough to drink. At one point, I feel them talking behind me, I turn around and see my boyfriend's friends who were looking at my skirt. I turned around again and threw my ass back, then one of them approached me and first touched my back, then put his hand between my legs, opened my thong and put two fingers in my pussy. It was only a few seconds, but we cheated on my boyfriend and he never noticed