While the dominant male is giving anal sex to the receiver he defecates. The giver is defecating and not the taker, and therefore the giver is packing (it in) and shipping (it out). The name derives from the story that Uncle Sam Wilson of Troy, NY was a meat packer during the War of 1812. The initials U.S. were inscribed on the meat packages to be sent to the Army, and it became legend that the good meat was from Uncle Sam.
I really wanted to go the bathroom and have sex at the same time, so I decided to perform Uncle Sam's Pack & Ship on the toilet.
by Winclemo March 09, 2008