No, I don't like BMing. It's rude and disrespectful. If someone BMs me with an insult, I prefer not to say anything back, but obviously I gotta say something to those "special" no-nos. And even when I talk back, it isn't in an insulting way rather than a brutally honest way. Usually along the lines of trying to talk sense into them like "It's a game, acting like a 12 year old doesn't make you look very good" or something like that. Usually followed with "Lol u mad bro" and whatever but that's just confirmation that what I said got to their head to some extent, because they couldn't come up with a proper counter-statement other than a generic gamer troll quote.  

Honestly when there are trash-talkers in the chat, a simple "12 year old" line will make them quiet because you just brought the outside world into the fantasy realm of gaming, and people don't like that kind of stuff. "Trolls" have even been psychologically evaluated to have corrupt social tendencies outside of the gaming realm, so bringing stuff up like that really teaches them a lesson. Is it an insult? No, more like a brutal reminder of their behaviour. I don't insult or swear in chat because what makes the gaming world different? People are still people and some people need to be reminded of that.