How to tell this "friend" to stop disturbing me?

When I was in elementary school, I befriended all the kids that were "rejected" by the main crowd of the more popular kids. Yeah, I was a sort of "dork" myself. One day,a large, tough bully was about to beat me up when suddenly, along comes this friend of mine, a kid who's parents were poor Mexican migrant farm workers who lived in a little shack, and he grabs the bully and says: "don't you mess with my friends or I will beat the hell out of you! The bully never bothered me again. Sometimes a friend, no matter how unsavory, is a friend, indeed!