A verb that is used frequently in romance novels describing how a woman's nipple pops outwardly during a scene with a lot of sexual tension or just plain, old-fashioned sex.
Under the gentle but calloused hands of the stable boy, Thomasio, the Countess Fiora's desire grew obvious as her breasts swelled and her nipples pebbled.
scale of being stoned. not stoned but maybe just a little bit high. Pebble is a small rock hence where the scale comes from. when you have had one toke on a joint you are pebbled, not stoned yet.