double doppler 

Is when the male partner's balls repeatedly smack against the female partner's vagina while perfoming anal sex.

Martha really likes the double doppler effect when I am doing her up the butt.

double doppler by Frances Wates June 19, 2006

Double Doppler 

when both male testicles are placed in the female anus

I gave Sherri the ol' double doppler last night and my balls barely fit!

Double Doppler by dopplehoffers March 10, 2011