1. Exclamation used to indicate disgust in one's excessively lazy lifestyle.
2. Adjective used to describe a person who is habitually excessive, particularly in relation to food and drink, but also in relation to drugs, lethargy, and general sloth.
"Don't get toclose to Vincent's flabnasty mom. She'll chew your arm off! Flabnasty!"
My old teacher saved his whole platoon in Nam by jumping on a land mine -- but damn that crazy was fugnasty.
syn. = fugly, just ruder, to be used at the end of a sentence only, with a hard quick emphasis on the FUG part. This is astepping stone to the use of the F-word in more everyday contexts.