This is just trolling. You can make your argument without resorting to this sort of childishness.
Neither insults nor trolling is childish. That is not a valid argument and has been used ad-nauseam against both. It's fun to read if you're in the right mood, especially when it is on-point like here.
In your opinion, which I'd question if you think phrases like "
pasta fucking pizza wanking twat" and obscene 'your mom' jokes aren't immature dialogue. Hardly witty insults are they? Regardless of how fun you think it is, he's clearly doing it to agitate and it's unnecessary and derailing threads.
That is a very common, proper way, of using British insults. I don't see how culture-differentiated way of insulting should be labelled childish. Are American insults childish too? As long as he's primarily on-topic, the insults should be deemed proper-use of the posting function (and not derailing exactly because it's on-topic). Solely insulting posts are, however, likely to be derailing (but this doesn't have to be the case either). You can answer a proper question, with a proper insult and it's still a valid response. Regarding complete derailing, I'm certain that we have some observable instances of much worse members that are not being dealt with. So why should TMAN?