it's a person who is just acting stupid. They act so stupid that it's funny. You calling someone this makes what you were laughing at even more funny. (NOT MEANT TO USE IN A SERIOUS MANNER)
''HAHAHA, oh my goodness that is so funny imma go get some more food''
''Okay.....''
**KNOCKS OVER BAG OF PRETZELS**
''HAHAHAHAHAHA did you just knock over the pretzels you retarded clump of gas HAHAH.''
**EVERYBODY STARTS LAUGHING**