A Ball Wahl is a term used to describe what a male actually uses a Wahl beard trimmer for - to shave his balls. Contrary to the belief that the Wahl beard trimmer is used on the face, it is almost always used to shave hair in the public area.
Joe: Hey guys, I got a new Wahl trimmer in the mail! Can't wait to shave my face!
Sean: That's a Ball Wahl for your nuts you don't even have facial hair.
Joe: This is true.