For me, my main issue with rude people and bullies is that it costs us nothing to let “the other person” retain their dignity in any conversation.
So, for that reason alone, I’d never tell anyone that they’re nasty (even if they are) or that a dialogue is pointless.
What I have said is something to the effect of “there’s a good potential conversation here, but I don’t respond to comments that include insults, personal attacks or name calling.” Sometimes it results in an apology and a decent conversation. Other times it results in blocking someone. lol.
P.S. I used to have a close friend named Linda. It used to amuse me to call and say Hi Linda, it’s Linda. Apparently this still amuses me…