When Bill says his life is harder than Dipper's they decide to do some body switching. Dipper is 18 Bill is super old demon.
Mystery Shack Dipper's room
"Man oh man what a day!" Bill says walking into Dipper's room "You should've seen this guy twice my weight and I still knocked him out!" He boasted chuckling.
"Right but not as hard as doing homework and having peer pressure." Dipper said while reading the journal.
"Is that a challenge?" Bill said getting in Dipper's face she looks up surprised.
"What no! I'm not doing a challenge with you Bill." Dipper says shaking her head.
"Chicken chicken!" Bill called out doing the chicken dance and dies some chicken noises making Dipper glare at him.
"Okay this is the peer pressure I'm talking about!" Dipper said but Bill kept doing it making her get up "Fine!" She yelled.
"Fine what?" Bill asked smirking at his girlfriend's serious face "I'm fine is that what your talking about?" He said wiggling his eyebrows.
"Gah!" Dipper blushed pushing Bill's face "I mean I'll do your challenge!" She said clarifying.
"Good then let's get that magic carpet Ford has!" Bill announces taking Dipper by the arm running to Ford's room where the carpet lies.
"Wait that thing that made me and Mabel switch bodies?" Dipper asked horrified.
"Yep!" Bill said starting to rub the carpet creating static he poke Dipper making them switch bodies "Yah I'm Bipper again!" Bipper says.
"And I'm what Dill?" Dill says looking at herself well himself I should say.
"Well later!" Bipper says trying to fly but falls on her face.
12 hours later
"Wanna switch back?" Bipper and Dill asked. Bill's body all burnt up while Dipper's body looked all stressed out.
Cue audience laughter.