Mustard Eaters is a term used by Albert to describe players who have a yellow face, while the rest of the body doesn't.
Mustard Eater is an ongoing meme in the Flamingo channel. Albert uses the term whenever he finds a player whose face is yellow, while the rest of the body doesn't, making it look like their face is full of mustard. Albert makes jokes whenever he finds a Mustard Eater, such as "Mustard Eater! He LOVES mustard!"