A slut muffin is a phrase created by Bobbie Lee Silver to describe people who act/look like sluts, yet aren't completely disrespected due to a cuteness or innocence. Most accusations tend to be targeted towards younger girls who dress in revealing outfits and/or flirt with older guys. This is also used as slang to indicate that the girl is acting in sluttish way, but can be used as sarcasm to show an outfit is cute yet skimpy. It could also be used to describe boys who have many girls clinging to him, but is mostly refered to as a slut monkey (the male equivilent to slut muffin).
"Tanya is such a little slut muffin! She's only 13 and David is 18! How dare she grind on him!"
"Aw, look at the little slut muffin in her mini skirt"