One of my all-time favorites:

A Sailor is relieving himself in the head when a Marine walks in and steps up to the urinal beside him.

After a few seconds the Sailor finishes, shakes, zips and walks over to the sink to wash his hands. The Marine also finishes, zips-up, and walks to the door.

Just then the Sailor says, "Hey Marine! When I was in boot camp, they taught us to wash our hands when we finished!"

The Marine looks at the Sailor and says, "When I was in boot camp, they told me not to piss on my hands."