Mark

"'I used to know a girl, she had a dozen guys. One of them found out about it, beat her up so bad she ended up in a hospital on Guerrero Street.'"

Mark is Johnny's best friend, who betrays him and cheats with Lisa. Like Johnny, Mark enjoys tossing the football and jogging. Often times he would talk to Johnny about real estate while jogging, or work and sex while eating at a cafe.

Career
It is unknown what Mark does for a living, but it seems to get him good money, enough for Mark to contemplate moving to a bigger home.