For me one of my faves would be the first time I had anal sex with my then GF. We were at a HS party in a friend's house. Her parents weren't home so we went wild with alcohol. There were maybe like 14-16 people in the house. We got suddenly horny and went to the upstairs bathroom. We made out inside, I pulled her miniskirt up, almost tore her panties off trying to pull them down and suddenly I noticed I didn't had any condoms with me. We were too horny for even going outside the bathroom and asking someone for condoms so she bent over, spread her butt cheeks and said in an almost desperate tone "Fuck me in the ass". I took a baby's shampoo bottle that was near and put some over her tight pink asshole. I started fucking her and the new feeling of her tight, incredibly warm and differently textured hole almost made me cum instantly. She farted twice and apologized but that combined with her moans, groans and the fact that people were outside, gave me one of the most intense orgasms ever. I still get hard remembering the experience.