The use of the term "straight man" is commonly known in the world of comedy. The "straight man" within a comedy duo says the serious sounding lines which facilitates the "funny comedian" of the duo to use them as an opportunity to make jokes about them.

This is usually used for comedy teams. Usually one person is quite silly and strange, while the other is a little more serious. The classic example of this is old US comedy like Dean Martin vs Jerry Lewis or in magic Teller vs Penn

Or there is the meaning we use in this century... A person might say that they are a straight man because they are attracted to women, not men.