A sexual innuendo used to depict a female using a pop tart, preferably cherry or hot fudge flavored, to pleasure herself early in the morning while in the shower. The pop tart will obviously turn soggy. This is often considered a delicacy in high-class societies around the world and is always eaten by a significant other present during the pleasuring in the shower.
Michelle: "Katie, did you eat breakfast yet?"
Katie: "Actually, I did already. My boyfriend and I shared a shower pop tart this morning."