When two sets of partners engage in sexual intercourse at the same time. One pair fuck on the top bunk while the other pair fucks on the bottom, respectively

Anatidaephobia is defined as a pervasive, irrational fear that one is being watched by a duck. The anatidaephobic individual fears that no matter where they are or what they are doing, a duck watches.

Anatidaephobia is derived from the Greek word "anatidae", meaning ducks, geese or swans and "phobos" meaning fear.

Bunk and fuck put together into one word, you do the math. Can be used in any way whatsoever, but usually used in negative terms.