Someone saw my RT and used that as an excuse to be a jerk in my inbox? I've never had that happen before, but I'd simply ignore them and leave the conversation; if what they said was particularly insulting, I'd report the message too -- if they're being toxic to you there's a good chance they're doing the same to other people.
I have had interactions where someone responded to my thread and I sent something back that they saw as a reason to rant at me, and nowadays I do the same as the above: report it if I think it's reportable, leave the convo, and ignore the sender. Giving them any more attention is a waste of your time.
Of course, if I've been playing with someone for a while and they say something that comes across as rude, I try to talk it over first. Knowing my RP partners, it's typically just a misunderstanding that can easily be resolved.