Really annoying ex-boyfriends

Well, I'm not speaking of my own experiences. Never really had an ex-ex-boyfriend (had some flirts, but nothing really serious). But my sister has.
And he's being a real pain in the ass.
They had a relationship for almost two years, but my sister always had the impression he wasn't being honest with her. I never trusted him, though...
Anyway, a few weeks ago she discoverd the nasty truth. He had been lying and cheating all along, acting like the bastard he is. So my sister kicked him out. With me cheering her along. Fi-na-lly he was gone!!!

Well, no such luck. Now he keeps sending her text-messages. Acting like a total innocent. Keeps her asking why she is so mad at him. Stupid asshole!

So, my question to you: Did you ever had a really irritating ex? How did you handle the situation? Did he/she came crawling back?

Cheers,
Andi