A few years ago I remember watching a standing ass-surprise for Kimberly Cummings. She was with a bunch of guys in a kind of gang-bang. At one point Kimberly was standing with her back to some of the guys. And one of the balding guys all of a sudden ran accross the room towards Kimberly yelling at the top of his lungs. When he made contact with her, his cock disappeared between her ass-cheeks. For some reason, Kimberly tried hard to restrain herself from giggling and laughing. And to this day I keep wondering did this guy actually penetrate Kimberly's ass? Or did he just slide in between her legs and made it look like he was inside her ass?
This scene also left me wondering why is it that porn movies almost never show a guy penetrate the girl's ass when she is standing upright without bending over?
Standing anal penetration is definitely possible and perhaps not uncomfortable. Once in a while you see the girl lie down in the prone position with her legs straight out and have a guy ride her ass like that. Her anal penetration wouldn't be any different if she was standing up instead of lying down.
The appeal of standing-anal position for me is its potential for ass-surprise on an innocent-looking girl. In series such as 'Breaking 'em In' young innocent-looking women often do it with two or three depraved guys. And it would be interesting to see the girl start innocently kissing and necking with one of the guys, while another guy quickly lifts up her short-skirt, brushes aside her panties, and disappears his cock inside her innocent ass just as she looks over her shoulder with a gasp to see what's going on back there.
Such rude violation of an innocent lady would definitely look a lot more exciting and hot than all the hair-pulling, choking, and slapping you see in some of today's movies.
Perhaps the lady would need to get some anal lubrication before the start of such a scene in order to make her ass-surprise sexy and possible. But going straight to anal without any anal foreplay is definitely possible, at least on film. A good example of such action is Katsumi's scene in 'A2M #9: The Art of Ass to Mouth'. Very early in this scene, one of the guys brushes aside Katsumi's panties and disappears his cock inside her sexy asshole in the blink of an eye. No foreplay and no preparation. One second she has panties on, and the next second the big guy is deep inside her ass.
I sure hope to see a lot more standing-anals than I've seen in the past. Perhaps it's not the best position to show off the girl's ass. But it is the best position to show a man surprise the sexy lady's ass.