The greatestexpression ever created in the entire universe, it can be used in any language and at any point in time. Most commonly used after kicking the crap out of some or in awkward situations roadhouse is truly what will save our world
To casually, but vigorously and lustfully, engage in promiscuous sexual or pre-coital activity, usually with a person with whom one is not in the least bit romantically involved. It's what "cheaters" and "fuck buddies" do. The implication is that the couple meet discreetly and stop by an outhouse/ roadhouse/ motel etc. to do their naughty business.