I'm basicly in agreement with dphoadley, and had written this phrase before I read his post.
 
"Eat yer heart out KP"

Perhaps "Eat your heart out" sounds rude, or even macabre in Italian, but in English, the expression is often used jokingly to mean something like "Be consumed with envy" I might say it to rival fans at a football match when my team has just scored 2 - 0, or  I might say it to a friend when I have just beaten him convincingly at a game of pool, or when he pulls up in my drive in his rusty old car to see I have just bought a new one.

In the above phrase I deliberately misspelt "your" as "yer" which gives it a kind of low class vernacular tone, and tends to reinforce the idea it is said jokingly, as feigning an accent does tend to suggest this.

I also like raven's 'Kitty who?'.

It has an air of ultimate disdain, but at the same time we realise  that she does know who Kitty  is, so the comment is seen as over stated and not entirely serious.

"I don't give a damn about K. P."

sounds too sharp and bitter, not at all joky, though ""Bite my dust, K.P.!" or ""Eat my dust, K.P.!" are OK.