Kevin Gallagher aka Lil' Kevin (portrayed by Kyle Davis) is a rapper who dated Dee Reynolds in season 3. Dennis and Kevin went to the same elementary school together and Dennis tells Dee that Kevin is retarded. Dee dumps him and later discovers he is not in fact retarded when he slams her during a rap song. Kevin reappears in season 6 as one of the potential fathers for Dee's baby.
Lil' Kev lives with his mom, doesn't drive, calls cartoon shorts "movies", drinks juice boxes, and wears his T-shirt backwards.
These traits gave Dennis and Mac the wrong idea that he was retarded, when in actuality, he's just simply childish.