it's a... thing

it's a (type of person) thing

Something is only understood or appreciated by a certain type of person or group of people. I know it seems like they're really insulting each other, but they're actually being really friendly. Banter like that is just an Irish thing, I guess. I can't help but stop at every bridge I cross and examine the workmanship. It's an engineer thing.
See also: of, thing

it’s a... thing

(informal) it is something that only a particular group understands: You wouldn’t understand the attraction of fast cars — it’s a man thing.
See also: thing