In order to trash talk opponents in Bitlife, you will need to first be a pro player of any kind of sport in the game. However, if you are trying to complete this week's challenge, you will need to be a basketball player and a pro one too.
Once you are a pro player, by going through the necessary steps, high school sports and then college, and so on, you'll be able to trash talk through random events.
During these random events, you'll be able to choose the option to trash talk your opponents, but only if you are in the pro leagues.
So if you want to become a pro player, make sure to build your athletics up to join one of the various high school sports. Age up, and you will eventually become the captain of your team and graduate from high school.
Once you graduate from high school, apply to college and then join a college sport, and you will eventually be able to get drafted or join a pro team later on.
If you don't get drafted, you can always try manually joining a team via the special career tab sports section. That said, when you are finally a pro player, just age up, and you will eventually get the option to trash talk.
But before you use the option, it's worth noting that you can cause other players to attack you. Because of that, it's not ideal to use this option beyond challenges in the game, as they can result in a decrease in stats and possibly being injured.
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