a combination of the words slut
and muffin. a less harsh word used to call your friends slutty without offending them.
Friend 1: "OMG! I love you girl!"
Friend 2: "AH, I LOVE YOU, TOO! But sometimes you can be a real sluffin!"
Friend 1: "Yeah, I totally know. I shouldn't have hooked up with those 4 guys last night!"