Who is my grandpa?

One day I was picking up my students after lunch. Johnny and Sammy were arguing. I approached and asked, "Boys, what is going on?" Sammy said, "Mrs. Lyons, Johnny said my grandpa has hairy balls." I had a very shocked look on my face and said, "Johnny, what did you say?" Before Johnny had a chance to respond, Sammy said, "Mrs. Lyons, I don't even know who my grandpa is!"