The act of dressing oneself and an accomplice in furry animal costumes and having them piss, shit & come on you. The soiled party is known as the "jiffee"; the soiler as the "jiffer".
As seen in "Stars Wars: The Return of the Jedi":
C-3PO - "They seem to regard me as some sort of...god. It'd be alright if I could only stop them jiffing all the time, look there they all go again!"
The sexual, and sensational, act of stuffing Jif peanut butter into your partner's holes then having sex in said hole. After the male climax's in the Jiffy filled hole, the male then proceeds in sucking out semen infused Jif and either can eat it or share with his partner.
Person 1: "Dude, after Jiffing with Jessica, my mouth tasted like peanut butter for a whole day!"
Person 2: "That's crazy that you two really Jiffed together. I really want to find someone willing to do some Jiffing."