Cabbages are not projectiles
We fully understand that working retail isn’t the most exciting or fulfilling job. However, it does pay at least some of the bills, assuming you can keep your job until the first paycheck. However, this guy wasn’t going to take nonsense from nobody, so after encountering an annoying customer, he threw a head of cabbage at them.
A cabbage seems like an odd choice for a weapon until you realize that they’re easy to hold and aim at someone’s head (not that we know). The manager asked him the leave, which was probably a huge bummer for his co-workers since that might’ve been the most entertaining moment in their lives.