This is a group of seedy people your friend hangs out with when he is not hanging out with you or your primary friend group. You wonder how your friend came to be acquainted with these people and how he could possibly enjoy their company. Oftentimes, your friend is admittedly embarrassed that he is associated with his Bridge Friends. Bridge Friends are generally shady people you don't want to be around.They are also typically slow, have terrible senses of humor, and often wear jean shorts. These are the type of people you would expect to hang out under a bridge.
Friend 1: "Where is Jerry?"
Friend 2: "He said he is going to some underground luau with his Bridge Friends."
Friend 3: "Those guys are creepy, I don't know why he hangs out with them."