First time for me just sort of happened. GF and I were having a good fuck with me doing her doggy. We weren't in a rush and I was spending time rubbing her asshole while thrusting into her pussy. I then reached over for some lube and stuck a finger in her ass. I stopped thrusting and asked her, "so do you want to try it?". She said yes. She always wanted to try it at least once. I got her ass prepped good with lub and finger probing. Then slowly inserted my cock. Just a bit at a time. In a bit, withdraw, and back in untill I was fully in. Had a nice slow pace. Felt great and different because of the tightness. She was really enjoying it. Eventually shot stream after stream of my cum into her ass. I collapsed on her. When my head finally cleared. I cleaned her up so she could walk to the bathroom without cum dripping out of her ass. It was fun.