So I just had an experience where my practice partner, of all people, was giving me some trash talk. Now, sometimes it's all in fun, but he's better than me, and when he repeatedly beats me and trash talks me as he's decimating me really doesn't make me want to play again. It's possibly time to find another practice partner - aren't they the one to help you improve and want to play again and again?
I know that some people do this on ladder, although I don't know why. Does it make them feel big to make someone else feel small? Sure, maybe they are just figuring out what this whole "social conduct" thing is about, but for the rest of them, they're just ruining someone's day.