There are two reasons to be laughing while watching "Humpday," one of the year's most refreshing films. The first reason is because writer-director Lynn Shelton offers up some wise and clever ideas regarding 21st century relationships, both romantic and platonic. The second is pure shock, which is not to be confused with disbelief, because everything somehow rings totally true. In "Humpday" an old friend lands on a man's doorstep in the middle of the night. Andrew (Joshua Leonard, who charmed in "The Blair Witch Project" then disappeared) is the vagabond, bursting with tales of travel and adventure. Ben ("Baghead" director Mark Duplass) is settled down and planning to start a family with his wife Anna (Alycia Delmore, this film's sly MVP).

There's a simmering of good-natured competition between these two men, which comes to the fore the day after a wine-and-weed-fueled party during which they drunkenly agree to film gay porn together as an artistic statement. The sober conversation is funny and mesmerizing; neither is dying to have sex with the other, but no one will back down. Ditto for the giggly suspense of the scene where Anna figures out what's up. It's flawlessly improvised scenes like that, along with the naked - as it were - revelations of the final "act" that keep your jaw on the floor in the best way.