Oh, now this is a good one. I suspect he will say something ironic but I'm not sure what.

Yes but Damon can do 1000x better I'm, sure it will be a memorable quote!

It would be hilarious if the first thing he does is to bite her then give her some snarky comment!

Then Katherine can return that by saying what he did to Elena as it's likely Elena will be jealous because biting/blood sharing/blood sucking is kind of intimate.

Hahaha yes good one. I think Katherine will still be very Kathriny obviously so she'll bite back with some sought of snarky response!

When Katherine shows up knocking on the Salvatore's front door, I believe that Damon will likely say something like, "Well, look who it is.  If it isn't the big, bad vampire Katherine.  Oh, wait a minute.  That's right.  I seemed to have forgotten.  You're no longer a vampire.  You're no longer immortal.  With that said, it would be in your best interest to leave."

Does that sound something like Damon would likely say? 

Just spat my drink everywhere litterally lmao that sound exactylike damon but maybe:

Loosing your touch, correction imortality evil one!