someone that is named Griffin that has a chipmunk looking face.
Hence, Griffin and chipmunk put together.
and or, someone named Griffin that thinks he is a player and uses cheesy lines to get the girls.
and if it is a girl named Griffin, she is a lesbian.
"man, that guy looks like a Munkfin!"
GIRL: "i was totally walking to fourth period and Kyle came up to me and started acting like a Munkfin"
Makenna: "Uhm, Haley?"
Makenna: "We've been friends for a really long time and i really just want to be your girlfriend."
Haley: "EW! Stop being a munkfin!"