please help my vertices find their way home :(

so, okay. this is my first time really working with blender, please bear with me here.

i’m trying to get a skeleton rigged on a model to stick that baby in gmod. everything was going awesome until, uh, this?

i’m in the process of painting weights and suddenly (or maybe i just didn’t notice before??? but i don’t think that’s the case), pretty much every arm joint in the skeleton, when rotated in any direction, does this to THIS arm in particular.

lowering poly count didn’t help, and neither did removing doubles of vertices. any help?? i haven’t found any other options online.

i am more than willing to provide any information you need. thanks!!

provide the .blend please.

you dont need the blend for this. its clearly a weight painting issue.

why so little details then? why didn’t you provide visuals of those details? Which bone(s) are those vertices weighted to?

True, nobody needs a .blend because it’s not anyone else’s problem. But for anything more helpful than “it’s a weight painting issue”, a .blend is needed. It’s always needed. If for nothing else, to speed up replying with actual details because explaining with screenshots takes less text than without.