I recently came across a user profile that I felt was offensive and was wondering there are any rules in place for the type of content one can post in your profile. Is everything OK, even, say, pornographic content? For me this would be hard to accept and seriously rethink if I should continue being a member of Stack Exchange.
User profiles are granted as much liberty as possible, but there should be some common sense in terms of the content being posted there. User profile pictures especially, since these make their way into the mainstream site content more readily than the description (in the user flair).
If you have reasonable doubt as to the social acceptance of a user profile, share the information with moderators (flagging any of their posts as "other" and explaining the concern; if they don't have any posts, bring it up in chat).
If an average person would clearly take offence at an avatar or profile due to:
- Graphic violence, nudity or sexual content
- Targeting of any race, religion, gender or ethnic group
- Exceptional cases where very poor taste would be likely to offend most people
... then you should flag it for moderator review.