That's the thing... we don't really worry about what is "allowed" here. The blockchain is a bit of a lawless frontier. We do have a developing set of community standards, though. If it's particularly rude, just use the "nsfw" tag and most front-end sites should make viewing optional. Unless you're plagiarizing, treating people abusively, misusing tags in an effort to get more clicks, or otherwise being a jerk, you're probably in the clear.