I've seen my share of moderator/administrator impersonaters around- and to be honest, yeah. I would laugh at them in amusement and make my own little comments in a party chat that I am in so very often.
They are ridiculously annoying, but I suppose you all know that. However it's best not to provoke or make fun of them- or at least not /infront/ of them. Otherwise you'll just be sitting there, listening to their pointless rambling about how they will ban you and what nonsense, probably thinking that their silly threats might be capable of scaring you.
But, as several others stated before me- it's best not to feed them, and in my opinion: If your gonna be a little cruel like me and laugh, point and mock- do it behind their backs, at least they'll never know then, and what you wanted to say would of been said, and their feelings would not be hurt- not to mention their rambling would not of gone on. The best thing to do immediantly after would be to take a screenshot though, and send it to actual administrators and moderators if you feel it is serious enough, and then just allow them to review over it and pass their own judgement.
BlackiOuti