In Back 4 Blood's Beta there was an unintentionally defective ladder in a warehouse section of the game that accidentally caused the players character to die upon using it. The game's devs decided to poke fun at this, after fixing said glitch in the final release of the game, by adding graffiti on the wall adjacent to the ladder that tells player to use caution when using it. They also had Mum comment on the "suspicious" ladder when she approaches it by telling the other characters to be careful on it.
Contributed by PirateGoofy