Green’s Dictionary of Slang

big deal adj.

[big deal n. (2)]

important, urgent, impressive etc.

[US]H. Ellison Web of the City (1983) 25: Lemme alone, and I let your big deal Prez alone.
[US]D. Ponicsan Last Detail 3: It’s something really big-deal I think.
[Aus]D. Maitland Breaking Out 55: I suppose you’re a big-deal crim.
[US]J. Wambaugh Glitter Dome (1982) 46: It wasn’t as though it was some big-deal homicide anyway.
[Aus]M.B. ‘Chopper’ Read How to Shoot Friends 53: The big deal greyhound blew his monkey muscle at the time trials.
[US]N. Walker Cherry 8: And you might be crazy, and you might have a gun, but even then it’s usually no big deal.