Not a gamestop employee, but I worked at a subway that was in the same parking lot as the gamestop. After working at that subway I became friends with some of the managers at that gamestop. I would give them free food, they would give me discounts on games.
Anyways, one day one of the managers comes in after his shift and I ask him how his day went. He said that it went fine until the last few hours of his shift. Apparently some guy came in asking to return a game that he got from a different game store (not gamestop) and asked for a full refund. When the manager said that the guy couldn't return it because it was from a different store, the guy went apeshit and started yelling and destroying stuff in the store. Then the man pulled out a knife and started going to town on a cardboard cutout. After doing that the dude left without saying anything to anyone.
Manager says that the dude was probably high/drunk when it happened.
Source: https://www.reddit.com/r/AskReddit/comments/bicr5z/gamestop_employees_of_reddit_what_are_some_of/em00e13/