What would be some good, class themed strange parts?

Like the Posthumous kills parts, I know it can be used on Rawket Lawnchairs as well but really, most people use it on their flamethrowers. So what would be good parts for other classes? (Preferably Spy)

Edit. Sorry for the confusion, I meant parts that don't actually exist. Like a concept thread. So more like the stuff spupy posted:

Spy: "Pyros killed while you are on fire"
Spy: "Charged medics killed"
Spy: "Razorback snipers killed"