I'd pace back and forth, motioning dramaticly while saying something like
"I can't believe it! Has it really come to THIS!? Oh ho ho, but it has, hasn't it? Of course you know, this isn't personal. It's just something I have to do. So no hard feeling, right? Of course not, you always were the reasonable sort. Another time, another place and who knows how things might've turned out. We could've been friends, or better yet, never met! Then it'd be someone else's head on the chopping block. YesyesnonoNO! You just HAD to meet me though, didn't you! You're fault you're fault! Now because of what you've done I'm gonna have to get rid of you and make a mess because you know noone takes it seriously if there's no mess an- OH GOD THE STAINS! You'll pay for those!"
Might as well have fun with it, right?