get over on

Possibly from get one's leg over.

get over on

1. (transitive, slang) To have sex with.
   • 1994 November 14, Cornelius Plantinga Jr., “Natural born sinners”, in Christianity Today, volume 38, number 13, page 24:

     For Northton's young males, to " get over " on a woman -- that is, to lure her into sex with vague promises of love and marriage; to get over on a woman and, particularly, to impregnate one (or three or five), and to " get away without being held legally accountable for out-of-wedlock children " is to prove strength, virility, and status. To a number of underclass youths, love is only another hustle.

2. (transitive, informal) To take advantage of.
   • 2008 August 17, Paul Tough, “A Teachable Moment”, in New York Times, page 30:

     Stewart and his classmates gave Schmitz a hard time when she first arrived.' We tried to get over on her, but she always cracked down,' he said.'