I feel like this question is a bit too general, you can make fun of people and their weaknesses as an attack, or as social bonding. So I want to say that it isn't bad in general.
When me and my friends go around making fun of each other, so long as none of the jokes are particularly harsh (like, if they focus on peripheral issues) then I don't feel like any status attacks took place, it seems like its just humor that happens to involve us.
This seems to suggest that attacks are a completely disjoint category from humor and/or social bonding.
I suppose this might be a purely semantic thing, in which case I have nothing useful to add... that is, if you're just saying that if a friend does it we don't call it an "attack," even if that's what we would call it from somebody outside the group, that's fine.
But semantics aside, the same action can be both an attack and humorous and a form of social bonding.
Similarly, in some social circles fistfights are pretty common among friends. Such brawls are certainly attacks, but that doesn't preclude them also being good fun. All a question of what you enjoy.
When you make fun of someone, you are probably degrading their purity and disrespecting them (if we look at the results from the lesswrong thread on yourmorals.org, we can see that many of us consider purity/respect to be far less morally significant than most). Yet, making fun of other people does not intrinsically reduce their "utility" - rather - it is their reactions to being made fun of that reduce their own "utility".
This, of course, does not justify making fun of people. Every negative action is only "bad" due to people's reactions to them. But in many cases, there is little reason to be upset when people make fun of you. When they make fun of you, they are gaining happiness over some weakness of yours. But is that necessarily a bad thing? It can be bad when they make fun of you in front of others and proceed to spread degrading information about you, causing other people to lose respect for you. But they could spread that information even when they're not making fun of you.
Many people find it unusual that I actually laugh when people make fun of me (in fact, I sometimes find it uncomfortable when people defend me, since I sometimes even value the message of the person who's making fun of me). I usually find it non-threatening, and I'm even somewhat happy that my weaknesses resulted in the elevation of someone else's temporary happiness. I wonder if any rationalists feel the same way that I do. Of course, I will refrain from making fun of people if I think that they will be negatively affected by it. But it does make me wonder - what would it be like if no one cared if they were made fun of? Certainly, we must react to those who spread degrading information about ourselves. But does it really matter if others laugh at it?
Of course, the prospect of amusing one's recipients is an incentive for some people to spread degrading information about you or your friends. So that may be one reason to counter it. On the other hand, though, laughter is also an incentive for people to spread degrading (and potentially true) information about your rivals. Perhaps people somewhat recognize this, and are frequently somewhat hypocritical about this (not that hypocrisy is intrinsically a bad thing).
PS: I wonder how laughing at other's weaknesses fits in with Robin Hanson's norm-violation theory of humor. Other's people's weaknesses aren't exactly norm-violations.