When in an aquatic environment, such as a hot tub or pool, you and your bros take turns vigorously waving your hand in the direction of a bro's genital region to stimulate sexual gratification. This is best done when there is no female present. To clear up any discrepancies about ones sexual orientation, the act of wave whacking is non-homosexual, because there is no physical contact with the other bros body.
see also: dutch rudder
So the other day in the hot tub, Jerry was feeling down about himself because of a girl, so I helped a brotha out and gave him a wave whacking.
When my friends and I have a rough week in school, we take turns wave whacking each other in the hot tub.
After a late unsuccessful night at the club, sometimes you need a bro to wave whack with.