While working in a small computer store one day I had a customer walk quickly into the store and right up to the counter.
Customer: “I want to buy a mainframe.”
Me: (playing along with the “joke”) “I think I have a couple of them out back.”
Customer: “Good. I need a mainframe because I want to learn how to program in COBOL. I’d prefer a Pentium mainframe, if you have one of those.”