I guess I'm one of those two cuz I've done it, of course when i have it was when i was pretty young. The thing about it is, you cant really get that much in your mouth, because your body just cant twist itself like that (if you even can get that far). I've found I like good old fashioned masterbating with the hands much more satisfying just because, no matter what, you'll never be able to do yourself the way your partner can. I dont really try it anymore. But anyway, if you really want to, its better not just sitting there stretching your neck, you gotta get on your back, pull your legs up, and just try to suck. This can be pretty painful for your back though. If you ask me, just dont bother.