Lionel, it's no secret that Shawn and I went through a pretty brutal breakup. Now, things could get ugly. And if a punch gets thrown, well, I need you to take it.
Lionel is a rather large, nerdy-looking student at John Adams High. Cory decides that Lionel is his new best friend when he and Shawn "break up" after having a fight about which college to go to. Cory tries and fails to make Shawn jealous with Lionel, notably by taunting him by eating "another boy's grapes."
Shawn gives Lionel tips about being Cory's best friend, such as letting him win when they play basketball and making sure he stays hydrated. He does, however, warn Lionel to never eat cake in Paramus, because that is his thing with Cory.