my ex. again.

i think everyone has an ex that they wish would leave them alone. mine decided to IM me again today. i broke up with him last september after dating for three months, and for some reason he still tries to talk to me.
i defriended him a few months after the breakup, because the temptation to facebook-stalk him was almost as annoying as he was. even after months of my ignoring his messages, he'd still IM me and ask me if we could talk, or if i had a problem with him, or various little things like that, so i did the most logical thing possible: sent him an email. a cold, PR-toned email signed with my professional signature. you'd think that would be some sort of signal, but it appears not. he's IMed me twice more since then, and while i know he just wants to be friends i would prefer not to be. we weren't friends before we dated: why should we be now, when i know that we have little in common intellectually or in any other regard? if it wasn't worth it to me to maintain a long-distance relationship, when i presumably felt something for him, why should it be worth my while now to begin a friendship that can't possibly function?
i understand that it's difficult to have someone drop out of your life entirely, particularly if you dated at some point, but by the same token it's difficult to have someone show up in your life periodically when you don't want to deal with them. and i do realize that this post sounds bitchy, but anything that causes me any stress or irritation gets removed from my life. it's the healthiest way for me to be.