a guy thing
slang Something that is said to be done or understood primarily by men. A: "Is being late just a guy thing?" B: "No, your boyfriend's rude." It's a guy thing, Claire—you wouldn't understand.
guy thing
n. something that appeals to men; something that men do. We just do it. We don’t know why. It’s a guy thing.
girl thing/guy thing
Something particularly appropriate for or appealing to a girl or guy (woman/man). Girl Thing was the name of an all female British band popular in the late 1900s. This slangy sexist expression dates from the same period. For example, “The Monday night football games are definitely a guy thing,” or “Shopping for jewelry—that’s a girl thing.”