Some managers go overboard, but I kind of feel like trash-talking is to be expected, as long as it's not too personal or offensive, and provided that you have at least some level of familiarity with the rest of the managers.
For instance, one guy in my league made a gripe last week about how Lidge killed him one day with an ERA of 54.00. I promptly responded with "that's why you don't take closers in the first round". (yes, he took Lidge 10th overall.)
We are friends in real life, so it's cool. Things like that pop up in our league all the time - one manager was crowing about how well his team was doing, so we all told him to enjoy the Shelton boost while it lasts. More or less harmless stuff.
I can never figure how people get so worked up over fantasy baseball.