What does 'meathead' mean?

Answer 1

Meat head is a pejorative or slang term used to describe someone who has done something ill-advised, poorly thought out, or something that can be interpreted as generically dumb. It is often used playfully as many people choose more drastic and vulgar terms.

Answer 2

A derogatory term given by the predominantly slothful population to someone who strives to excel in a sport, usually bodybuilding or power lifting, to infer that said person is mentally inadequate and therefore subject to ridicule.