Green’s Dictionary of Slang

ass-kissing n.

also butt-kissing
[ass-kiss v. ]

(orig. US) sycophancy, toadying.

[US]M. Curtiss Letters Home (1944) 23 July 85: I was disgusted with the ass-kissing.
[US](con. 1944) L. Giovannitti Prisoners of Combine D 119: Ass-kissing doesn’t do any good around here.
[US]‘Iceberg Slim’ Pimp 60: The ass-kissing of the few who had solved the riddle.
[US](con. early 1950s) J. Ellroy L.A. Confidential 17: A transfer to the Bureau will take years and lots of ass kissing.
[US]E. Little Another Day in Paradise 71: The maitre d’ [...] does an excellent job of ass kissing.
[UK]Indep. on Sun. Culture 26 Sept. 9: Air-kissing and ass-kissing and general falseness and fakery.
[UK]Guardian Editor 7 Jan. 10: But then again, my personality isn’t conducive to butt-kissing.