Green’s Dictionary of Slang

(US) a general intensifier; also as adv.

1977		(con. 1969) M. Herr Dispatches 12: We aim to make good and goddammit sure that if those guys try anything cute they won’t catch us with our pants down.
1978		R. Caron Go-Boy! 154: You’ll all dig that goddammit hole or goddammit you’ll all end up in the goddammit cooler!