Slang, possibly from the end of World War II, but it was certainly used by the US Army during the Vietnam War. It means a heavy or awkward load in adverse or difficult circumstances.
When they first heard it, the expression “humpin’ the pig” the word humpin' caused a certain amount of consternation among reporters (see humping). The pig in question was not a pink bacon producer or an officer of the law but nickname for the M60 machine gun, so the grunt they were interviewing would have been a machine gunner.
With all the shit we humpin' on patrol, whoever called us light infantry musta had a goddam weird sense o' humour.
Either that or he's some fuckin' REMF who's never been out in the boonies.
When a girl or guy that has a boyfriend/girlfriend and has sexual intercourse with another girl/guy, or when they don't have a boyfriend/girlfriend and they just have sexual intercourse with a person without a label.