Green’s Dictionary of Slang

(US) a synon. for hell; usu. as hell, the phr. (1)

1966		Longstreet & Godoff Remember William Kite? 343: Hello, you ol’ cooter! What the hey!
1970		‘Troy Conway’ Cunning Linguist (1973) 64: What the hey. He loves best who loves last.
1979		Fantastic Four Annual 37: But, what the hey – nobody lives forever, right?
1987		‘Joe Bob Briggs’ Joe Bob Goes to the Drive-In 90: It’s ripped off from one of the classics of our day, so what the hey.
2005		A.T. Soffee Nerd Girl Rocks Paradise City 233: I get the feeling that she’s deliberately screwing up my drinking schedule, but what the hey.