Dude, all blacklisting someone does is remind the blacklister in the future that they didn't enjoy playing with the person they blacklisted. Ask Master of the Dead how many people he's blacklisted and some of the reasons for it.
@HaPi The Glorious Koala might be a better bet that MotD, he has about 600 on his BL last time I heard. But as for me, I'm usually pretty lenient on what constitutes BL worthy for me, I have three on my accounts (one on main, four (technically two) on alt), they're mainly just trolls.
EDIT: In response to Ox's image post (thanks), huge win streak =/= one win. Next time you try being cocky mate actually have the facts to back it up, Castle Bravo
Blacklising is like blocking on Twitter or unfriending on Facebook. You can do it for any reason you want and you should do it liberally. I blacklist all sorts of people. Anybody who starts trolling in chat or sending me creepy PM's or whatever, just blacklist them and move on.
I wish blacklisting hid their forum posts too, that would be awesome.