2. A person who is a fucking monster, for being slovenly dressed or hobo-looking in his dress. (Also See Fonstress for the female version).
Dude, you put on 30 pounds in the past week eating nothing but hoagies and mayonaise, you are a Fonster!
1. Also known as a sandwhich that consist of all available condiments.
2. That is quite a fonster sandwhich you got there...mayonaise, lettuce, tomatoes, ketchup, pepper, salt, vinegar, ham, cheese, pickles, onions, and relish.