Husband: How do you set the clock on this gadget?
Wife: Well, I have the instruction manual, but it’s all Greek to me.
Husband: Let’s just get the kids to do it.

Most English speakers don’t know any Greek at all. When they see something they don’t understand in the slightest, it might as well be written in Greek. If they don’t understand what someone is saying, he or she might as well be speaking Greek.