An uncommon mispronunciation of the word "COMEUPPANCE"
Typically used by those who have gone through their entire life not once ever seeing it spelled in its entirety. Interpreted as a well-deserved rebuke or penalty, or KARMA.
JOE: "I just boinked your mom"
GREG: "Damn you. You'll get your kermuffins"
JOE: "Dude, did you just say 'KER-muffins'? laughter, it's 'COMEUPPANCE'!" (laughter continues)
(JUST THEN a Velociraptor devours Joe)
GREG: "See. I told you..." (pretends to be a tree)