A maggot is a small, white, slimy thing.
An effective insult to those who have wronged you---especially when you give the above definition afterward.
woman 1: I can't believe he did that!
woman 2: Hon, he's a chauvinistic, cheating bastard: total maggot. Forget him.
man 1: Dude! Your wife was so tight when I fucked her last night!
man 2: What the hell? Fucking maggot! How was I stupid enough to believe you were my friend?