The guy's handle is literally 20 random characters, it's hardly harmful to joke about it. Why the anger?
Jokes in general are, if not explicitly against site norms, discouraged: "Comments should get more thoughtful and substantive, not less, as a topic gets more divisive." [1]
[0]: https://www.shrm.org/topics-tools/news/employee-relations/vi...
What a ridiculous presumption.
So either you made a joke that isn't funny or one that is offensive. Either way, there's your answer to why people didn't react positively.
He's a fine guy, and a fine coworker, but he's not the hot shit his resume progression would suggest.
I guess that's worth being taunted in graded school.