If you pick a hard counter to your opponent and they are struggling against you;
Don't gloat about it.
Don't brag, or goad them, or all that other "trash talk" "psych-play" bullshit.
You're already winning, you don't need to rub it into people's faces. And you're already kind of being a dick by picking a hard counter in the first place instead of a fairer match-up that would allow more player interaction. Don't be a douche by rubbing it in.
Love, a player who thinks tilting people on purpose is shitty behavior.