BUF

An acronym that refers to a large and gruff person, or possibly to a cartoon or video game monster; can be used with "fella" instead of "fellow."

Shallow, inconsiderate people might use the acronym BUF to mean "big, ugly, fat." This acronym is typically used by male dbags to describe women they consider obese and ugly.

You should likely never use BUF, and if someone has used this acronym in a conversation with you, you may want to explain why the acronym is inappropriate. (Alternatively, if someone has called you BUF, you may just want to tell that person to BTFO.)