Subject: Eruv.
Two guys have been learning together for 20 years. One of them is going to make a bar mitzvah so he says to the other one, “I am making a bar mitzvah and I would like you to come.”
“I’m sorry, I can’t.”
“But I really want you to come.”
“You don’t understand. I just can’t come.”
“But why can’t you come?”
“I’m not Jewish.”
“What do you mean? We have been learning together for 20 years.”
“I enjoy the intellectual stimulation.”
“But we learned that a goy that keeps Shabbos is ‘chayav mitvos.'”
“I never kept Shabbos. Every time I was ready to leave my house, I put a key in my pocket.”
“But we have an eruv here.”
“I don’t hold from that eruv.”