Person A and person B live in the same house.
Person B is always the more happy one of the two, so A is surprised when they come home one day to find B dressed in all black, with several spiked piercings.
A questions B's motives, but B only responds with "IT'S NOT A PHASE!" before running into the bathroom and locking the door.
A simply decides to go to bed, thinking that somebody must have put some drugs in their coffee (or whatever drink they like), and this is just the result of a drug trip.
