Can a guy stick his penis inside another guys butt hole?

He can try however inserting fingers very slowly and gently, using lubricant, and GRADUALLY working up to a fist. The thing is, we've been taught from babyhood to keep our anuses shut so we won't "poop our panties." So the first step in any sort of anal-receptive intercourse is unlearning, teaching ourselves to relax that muscle.

Yes it is possible. I work in a gay video/toy store. I have videos of guys fisting themselves, giving themselves head, and using bending Mr. Happy around to penetrate themselves with..themselves... I even have a video of a guy all the way up to both shoulders in 2 guys at the same time. Blew me away.