The Tap Rule 

The one prevailing law during a gangbang that creates order from disorder. After a reasonable period of time has passed, the gentleman who's "on deck" may tap the shoulder of the gentleman currently "at bat," and the latter gentleman must step aside and let the next guy have his turn.

This rule also works for drinking at a water fountain.

The Tap Rule was popularized during one particular scene (I believe it was No Holes Barred 4) where a certain anonymous man repeatedly ignored the aforementioned shoulder tap and was sternly reminded by one the men standing by to, "Respect the Tap Rule."

Rather than let the normally enjoyable experience turn to violent anarchy, the man relented and allowed the next gentleman to put his hoohoodilly in the female participant's cha-cha or whoopsidaisy, thereby preventing possible bloodshed.

The Tap Rule by nutman December 16, 2005

two tap rule 

When having sex (or making out) the two tap rule is a non-verbal way of communicating you are not comfortable with/don't like something your partner is doing. The two taps will let the partner know to stop, and go back to something you like.

Using the two tap rule- If you're partner puts their hands somewhere unwanted tap them twice on the shoulder so they know to move them.

two tap rule by Nineteen Percent December 19, 2017