Pay it forward - The new twist in the tale

Being sarcastic doesn't come to me naturally. I usually stagger after taking a hit, and try to make a come-back after a couple of seconds, if at all. So, the new year resolution from now on, and for the coming new year, will be to focus on "paying it forward", so to say...

Situation 1 (that recently happened to me):
Nasty boss: (on seeing me in office again, a day after my "official" last day at work): Oh, you're back (said with nasty/patronising overtones...)

Moi: (deflated, but trying to rally around desperately): Ya, I'm back with a bang!!! (how lame can one get :( )

So, I was wondering, what would have been a good response here? Let's take a few re-takes:
Nasty boss: Oh you're back!
Moi: Yes, it's really me! Believe! (has to be said with just the right air of patronization, else one may sound like a lunatic.)

Nasty boss: Oh you're back!
Moi: I'm not glad to see you too. But hey, we don't always get what we like. Deal with it. (this one could do with some subtlety, and can only be carried off if one is reallllly pissed off.)

Situation 2 (since it's not too great for my ego to try and remember my past slights, I'm going to use a situation that happened to someone else I know...):
Friend: (confronting another female who she knows has been talking about her nastily, behind her back): Have you girls been talking about me?
Bitchy no-gooder: No, the subject is not interesting enough. (Ouchh!)

Now, I know Friend's question was a classic invitation for sarcasm. What the heck, though -- she may have dug her own grave, but should at least be able to get out of it. What could Friend have said? Let's see:
Friend: Have you girls been talking about me?
Bitchy no-gooder: No, the subject is not interesting enough.
Friend: Guess it's less interesting than your routine subject of who's upper lip is less hairy.

Friend: Have you girls been talking about me?
Bitchy no-gooder: No, the subject is not interesting enough.
Friend: It reflects very well on me if dumb coots like you don't find me interesting (well, may not be the wittiest response, but some response is better than none, huh?).

Any interesting suggestions? Do give your two cents and help the world of the sarcasm-challenged :P