epithet
Explorer
Business 101 says do not ever insult or be insulting to your customers.
Business 102 probably says or should probably say dont Tweet it is just not worth it. He got angry and posted publicly, just not a smart thing to do. I am sure he will survive.
To continue with my apparent trend of the day (anecdotes from the last century,) I'm reminded of a burger joint on Guadalupe Street about a block from UT Austin, called the GM Steakhouse. Every day the slacker running the cash register would grab the microphone and insult people passing by on the sidewalk. He wasn't kind. Still, it was great for business because everyone he didn't insult was hugely entertained by seeing the ones he picked on get mocked without mercy.
I figure there are probably a few people who read that tweet and felt like he was barking at them. There are a whole lot more who, smug in the certainty that Mike wasn't talking about them, are tickled pink at the idea of a D&D "firing" some customers (as if that were a thing) that these folks felt superior to. For them, Mike's tweet was validation.
And for those few who do think of themselves as cootiephobe gatekeepers, I don't imagine many of them will quit playing 5e D&D or quit buying the books and stuff. Hell, they might think of it as a victory that they got someone in Mike's position mad enough to hammer out a poorly worded tweet.