In-game trashtalk is unsportsmanlike and disrespectful. Yelling "YOU SUCK (insert player name here)" after winning a round is just toxic. It's kicking a dog when it's already down, you won the round don't yell at the opponent it's just trash behaviour.
Stewie2k isn't a toxic outside of the game and the trashtalk before the games is much needed in the scene to bring excitement, but after winning nobody wants to hear you yell how bad the other team was, everyone has seen the JW+fnatic clip against NIP and no one can say they aren't fkn toxic. Just my two cents.
TL DR: Trashtalk before a match is cool, celebrating won rounds is cool, but insulting the opponents in-game isn't. That's the difference between Apex and Stewie2k, Apex celebrates and Stewie2k is disrespectful.