Green’s Dictionary of Slang

a general intensifier, extremely, very much, powerfully.

1965		H. Rhodes Chosen Few (1966) 184: To Blood’s way of thinking, women liked goodness and gentleness, but preferred a periodic asskicking raw man with that goodness and gentleness.
1993		J. Mowry Six Out Seven (1994) 391: He used to be ass-kickin cool!
1998		(con. 1986) G. Pelecanos Sweet Forever 67: The salesman [...] called it an ‘ass-kickin’, booty-whippin’’ picture.
2000		Guardian Guide 5–11 Feb. 65: A ranch hideaway where people pose as ponies for ass-kicking kinky fun.