The art of skillfully gesturing someone to roll down their car window at a stop light after witnessing them successfully pick their nose and eating it, by a using hand cranking gesture. When they roll their window down ask them if they would be willing to trade you "2 greenies (2-GREEN colored boogers) for a blackie." (a BLACK colored booger)

A) Letting them know you actually watched them the whole time, while they excavated around in their nose for their boogers & then ate them.

B) Embarrassing the fuck out of the nasty bastard for subjecting you to having witness that disgusting act they performed while in traffic, at that stop light.

C) Hopefully reminding them in not so many(unspoken)words, other than what you already said to them- it's a filthy habit that they should have given up as a small child.