One of the most important things when it comes to being able to make use of friendly insults and irony and so forth is to have some idea whom you are dealing with. I don't mean name and address and all, but from some previous meetings, you have had a chance to get some notion of when they mean it and when they don't.

That's one major reason why it's tricky with nameless GUESTs - by definition each new post by a nameless GUEST could be the first time you have ever "met" them. Posting as a GUEST without even a temporary handle involves rejecting the idea of any kind of continuity.

When an acquaintance comes up to you and slaps you on the shoulder, it's a greeting. When a total stranger comes up behind you and does the same, it's likely to be taken as an assault.