I think the issue for me is that a gamer tag can be anything that the user wants (well, within reason). It would be like someone signing up to Neowin with the same username Pres.Obama. It doesn't mean that they are President Obama, it was just a name that they chose.
Now if you had been playing against Honey Boo Boo (god, I can't even type that without my fingers cringing) and the player on the other end was mimicking her voice and generally playing like a 6 year old (hmm, given the skill levels of some players that wouldn't be hard to do) then I would have chuckled, but a username or gamer tag is just that for me.
But hey, that's just my view on humour. As the J&FS forum states, it's an individual thing.
Or maybe just the name broski.