In very poor taste.
On topic:
He was fired for stupidity, can't say stuff like that over and over.. you are a grown man, alcohol, drugs, entourage, money, fame etc whatever stuff happens in Hollywood doesn't excuse sheer stupidity.
I can't say if he is one or not just from some really stupid 'joke' tweets. But I'm 100% he is stupid, even if you did mess up with a joke why not delete it asap ? why do so many mistakes why leave them up for so much time if you knew you did wrong, the moment you got hired to do a giant movie "hey how about I deleted my retarded jokes about sensitive subjects that I put out in public".
Who knows what happens in the depravity of Hollywood, Gunn maybe uses that type of bad humor while drunk / on drugs with his groups of friends late on night in private.. even then it's fucked up, no one even talked to him about it.. but to say in public the heck is wrong with him. This all situation is it's very disappointing.
I really enjoyed his work and was looking forward to future projects, he didn't get to finish his trilogy, to bad I really liked his first 2 volumes.
Got to pay for hard stupidity no matter how you slice it. And I really hope it was just that stupidity and nothing more.