The double faced tummy wag 

an act of excitement or celebration;

When two men stand face to face, drop their pants and underwear, put hands on hips and "wag" side to side. This allows their penises to "wag" like a dogs tail simultaneously. The act may be escalated by standing close enough for the penises to hit one another to simulate applause.

Tim and John had just beaten Frank and Joe in the last match of tennis, and really rubbed it in when they gave a standing ovation via, the double faced tummy wag.

The double faced tummy wag by BuRnZy187 September 7, 2014