lol, these things.
Happens to me with my cousins when I play fighting games with them, mostly SSBB. Since I play a lot of fighting games, I have a general knowledge on playing on something between casual and tournament level, so when I do shit like Ganondorf side+B spamming on their wake-up, they get mad at me.
For the most part, this is what leads me to play multiple characters in any game, so I have a "character I'm interested in but suck with" and a "character that I'm CASUALLY GODLIKE with."
What you should do is start with characters you suck with, then when they start trash-talking, switch to your better character. If you win, trash-talk back. If you lose by fluke, you can now act like they no longer have the right to complain.
Either that or just troll around with your main, use them as live practice dummies for all your live-testing shenanigans.