The first time I ever fucked a girl up the ass was in my Senior year of high school. We had been having vaginal sex and oral sex for a while before then. Anyway, one night we were making out when I told her we should try something new. She agreed with a look of wonder on her face. I went into the bathroom and got myself all lubed up. When I returned (lube in hand) I told her to get on all fours. She did as directed and I moved in from behind. A quick squirt of lube on her asshole was all it took to get her attention. When I put my cock-head on her asshole she made an uneasy groan. I slowly popped it in and got the whole shaft in. When I started pumping she made moans of pain. I asked her if she wanted to stop, but she said "No, I have to get over the pain". After a few minutes of getting her ass used to being full, the cries of pain turned into moans of pleasure. She rubbed her clit as I ass-fucked her for about 15 minutes. We both had huge orgasms. For another good 6 months (until we broke up), I'd do her up the ass almost every other day. I can still remember how her little pink hole looked with my cock ripping it at the seams.