"1v1 me, I'll end you and your whole family" Why

What's the deal with people like this? I was playing some ranked and beat a guy with Lei. Within 10 seconds I had an invite to a private match where I lost 5-1, pretty good games that I enjoyed because win or lose, I love me some tekken.

Opponent instantly sends salty messages saying how good he is and how he has friends playing Lei who are better than me. I'm genuinely curious about these mentalities. People who do this, why? And people who meet these types of players, what are your thoughts?