a person who is acting in an
obnoxious manner, or is undesirable, this person really
grinds your
fucking gears.
Bob - "you see that girl ally last night? she was acting wild"
Jim - "yeah bro, she's a real fuckin mupbag"
Tom - "yo that kid Jeff jipped me on a dime
bag"
Lisa - "yeah, he's a real mupbag like that"