When 2 people use the same toilet at the same time. One person using the normal seating position on the bowl, and the other takes a seat on the top tank Upper Decker. Term originated at a warehouse in Holbrook, Long Island.
All the stalls but one were full, so me and Jose did BUNK BEDS in the only empty stall.
When you go into a QDOBA bathroom and the toilet is broken and full of someone else's poop. You have to poop really bad, so you poop on top of someone else's poop and toilet paper; with no choice but to leave the whole mess for some poor employee.
The other day I went to QDOBA and had to pull a bunk bed. Those pork tacos almost make me shit my pants every time.