Yeah, Fork you too!
It could be because SOStack Overflow has thousands of members with (limited) moderation powers.
It could also be because SOStack Overflow draws another kindpart of the public than e.g. a forum about some favourite boyband.
And, of course, because this site has so many active members at any given moment plus some smart algorithms to detect possible abuse, and thus abusive behaviour can be stopped real fast.
Plus, we have Meta Stack Overflow, where we can complain about anything that troubles utus at SOStack Overflow.
Still, peer pressure isn't enough to stop misbehaviour. Consider those Soccer Hooligans who misbehave during lots of all kinds of events, but mostly soccer sport events. Basically, these hooligans are just regular people and there are probably a few at SOStack Overflow and Meta Stack Overflow. But they organise themselves in groups for organized misbehaviour. There are online groups of forum hooligans who tend to misbehave at dozens of forums and the only reason why they're not harassing SOStack Overflow could be the moderation done by all members. Or maybe SOStack Overflow just isn't interesting enough as a target.
Because, strange as it sounds, SOStack Overflow might not be interesting enough for online hooligans to misbehave. :-)