The participant simply makes two fists and punches an upended mattress, punching bag, or other cushion. As a variation, punches can be aimed a catcher's mitt on the hand of an assistant, who may also role-play a provocative or demeaning person. Gloves may be wise, to protect the hands.
Rationale: Loosens up the back muscles, similar to hitting. The unambiguously aggressive nature of this exercise makes it offensive to some.
Source: The tradition of boxing of course has made using a punching bag famous.