I think you are referring to the "A-Pose" Glitch, yes it is an exploit or bug.
It's mostly used by "Friendlies" and it's kind of harmless since you can't use your guns unlike other glitched position exploits (*cough* *cough* ConTracker Exploit *cough* *cough*)
This glitch dates back around the release of the game, where you could type in console "join_class civilian" and it would make you an A-posing Scout, later this was patched but the community found a way around it.
You can kill them in the game if you find them annoying, since pulling out this glitch takes some time so yeah.
If you are referring to another one then i don't know which one it is.