A formation of military recruits that lines the nude men up in a
single-file line such that one
man's genitals are essentially pressing against the butt
crack of the
guy in front of him. This is done during induction between the
time the men surrender their civilian clothes and when they are finally issued their military uniforms, to allow the medical examinations and inspections to be expedited.
The Nuts to Butts line up also has the effect of revealing those recruits who enjoy the experience as they would likely sprout an erection and could be rejected by the commanding officers who wanted to weed out homosexuals.