I know this was asked before on the IMDb boards. He had the school friend who tried to make out with him, then in one of the first episodes when they were at a concert with the mechanic and his friend. Fez asked Eric if he would go to the restroom with him, and Eric says that only girls do that. Fez then pointed out this man and his friend went to the restroom together. Eric says something like, "I'll explain that to you later." What guy in the '70s would even know that?
I knew it but only because my friend was gay and he would disappear for a really long time after saying he was going to the restroom. I was thinking "What in the world could he be doing for that long?" I didn't have a clue.