A little dab will do ya refers to applying vicks vapor rub on the anal sphincter before having anal sex. The menthol in the vapor rub relax's the sphincter causing it to open up allowing the penis to be inserted easily. It also creates a warm sensation inside the anus making it more enjoyable for the female or male. It is always recomended to wear a condom before buttfucking someone!
Hick #1: Hey im gonna smear vicks vapor rub on my cousins asshole and fuck the shit out of her!
Hick #2:You know the old saying..."a little dab will do ya!"
girl: "My asshole hurts really bad from you ramming your cock up my ass!"
Dude: Try rubbing vicks on your bunghole before I fuck it next time...A little dab will do ya!"