Similar to the well-known rim job, or gravy rake, STP refers to the kissing/eating/licking aka SCOOPING of the ass aka POOP.
When using STP in the progressive tense, the -ing is to be distributed to the S and not the P. It is NOT Scoop the Pooping. It is Scooping the Poop.
Also acceptable: Essing some P.
In reference to the Carl Jung personality test, one who scores: I-introvert, S-sensate, T-thinking, P-perceiving, will be assigned the personality type of: ISTP. this person will most likely be more prone to Essing your P. If your P is in the process of being Essed, you most likely do not fit his personality type.
If you do fit this personality type, be sure to carry around Listerine. Also, beware of pink eye.
BF to shrink: "My girlfriend, shes been acting withdrawn lately."
Shrink: "If you really love her, you should STP. That's love."
BF: "You're right. I'll do it."
beachgirl09: "Hey. Lawlz, u should totally check out my new piks. 4rlz."
MacDaddy200:"U r rlly hot. Wanna STP nbd? lol"