Someone earlier suggested vulgar avatar's shouldn't be allowed
See:
1) Is nudity allowed? If so, to what extreme? To a non nsfw tag?
No.
2) Is NSFL allowed? [NSFL = Not Safe For Life]
No.
3) Is other adult content allowed?
Maybe.
If I receive (or anticipate receiving) several complaints about something, it's probably too much.
4) Are paid avatar campaigns allowed?
Yes.
5) Is copyright content allowed? How should copyright holders request deletion of infringing content?
You are not allowed to infringe copyright, of course. I have no way of knowing whether you have a license to use particular images, and it's additionally sometimes difficult to determine whether fair use applies, so I will not be proactively removing possibly-infringing images. The DMCA process is used.
6) Is racial / sexist content allowed?
Probably.
7) Is there a limit on 'annoyingness'?
Animation is not allowed, so I feel like it'd be difficult to create an avatar that is sufficiently annoying that I'd want to remove it.
8 ) Are 'imitation' avatars allowed? Ie wearing avatars of specific companies to give the false impression of representation.
Copying someone's avatar
in order to impersonate them or cause confusion is not allowed. But if you both use some generic picture of some famous person or something, that's probably not going to count, and using elements of someone's avatar for purposes other than impersonation will probably be allowed. Same for companies.
9) How should users report those with infringing avatars?
DMCA takedown notices or any other legal thing must be emailed to me. For other issues, post about it in Meta.
So animation wasn't allowed, but theymos allowed them anyway:
OK, APNGs are now detected. Old ones are grandfathered for now, in part because people have ongoing campaigns, but in the future I might (or might not) go through and remove them.
