When a woman lets two men ejaculate on her breasts, usually a D size or larger. They then race their ejaculate to see which one drips off first.
Chris: She was round the back of the pub, giving em a downhill racer!
by Logitic September 10, 2008
Sex act involving a person wanking two men simultaneously.
She gave Steve and Alec a downhill racer in the bathroom last week
by Jodiju March 20, 2011