If he wrote Bootstrap by himself, he's free to call every single user an idiot if he wishes, but when it's being released as a Twitter product, one would think Twitter would demand some modicum of respect to be shown. Can you imagine a Googler acting this way on the Chromium or Android projects? Yeah, there are decisions made on those where people aren't happy, but the comments aren't laden with zingers either.
My observation of open-source community dynamics tells me that being hostile is an effective way to lead a large community. I've noticed that contributors act more carefully around someone who is mean to people in general and that these people attract wide followings at conferences. (There are certainly exceptions, though, like Larry Wall.)
Can you imagine a Googler acting this way on the Chromium or Android projects?
I think fat is a jackass, but if he wasn't, I never would have heard about this project, which now has multiple front page articles on multiple tech sites. I imagine this is good for Twitter.
No, those are the exceptions. Being opinionated and ready to say no, however, is necessary.