To be honest, I think the amount of BM one experiences goes down as you climb the ladder.
All the BM I receive these days are on custom games where I try the other races for a change and when I lose, I get endless streams of,
"HA HA UR DIAMOND AND I WON. U SUCK"
Or somesuch. :<
Depends.
At the lowest level (wuts multiplayer??), people don't BM as much because everyone's terrible. At the highest level, people tend to be more professional (exceptions exist, naniwa, idra, etc). It's the players in between (all the way up to 000 diamond etc) that rage hard, because they're actually trying to be good, but aren't, and need to bust out that e-penis.
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