I become very playful and childish once I'm "in" with a girl. If I can't break through to this stage before a full-close, then it is innitiated once in pillow-talk/ snuggling time after sex. I'm very carefree and make it a point to create the vibe where nothing matters.
So to fart in bed isn't really that embarrassing. I might say "pull my finger" that way she knows what about to happen. Or, I'll make it as loud as possible and then just smile. Look, it's a natural part of being a human. I'm not ashamed to simply be just human. If she is pretentious or stuck up and think those kind of things actually matter than that's her problem. And if she can't see that as a weakness in herself than she deserves the fart. If she overreacts I simply ignore her emotions (as I know they are stupid and based in insecurity) and withdraw attention until she is behaving again.
I'll admit, sometimes girls just take so much work to train. But it's the only way a successfully fulfilling relationship will work.
This reminds me: one time, (and I love fucking with girls) I had this mLTR, and I was eating her out... get this: so I'm munchin' some rug and I pull her vag open with my fingers and blow her up like a fucking balloon. I literally filled her pussy with air! HAHAHAHA OH MY GOD IT WAS AWESOME!!! I'm cracking up just remembering this. She went nuts!!! Oh, it was great she sat there, pisssed the fuck off as she uncontrollable farted out of her vageen. Picture me, cracking up, laughing my ass off as she skirms and honkers at me, pathetically helpless as she uncontrollably farted. Oh god, and it lasted for a solid minute too!! HAHAHA it was sweeeet!
-Elation


