That line (which is not incredibly funny on its own, but very very funny when paired with the reply "Okay, we'll tell him Justin is coming") is from the movie Eagle vs. Shark. The tag for this movie is "love is awkward", and those three words easily sum up the theme of the film, which is like the ugly child of Napolean Dynamite and Flight of the Conchords. In fact, half of the Conchords plays a major role in Eagle vs. Shark (the Eagle for anyone who cares).
The soundtrack album to Eagle vs. Shark is greatly comprised of lines from the film, with some song filling by The Phoenix Foundation, Luke Buda, Age Pryor and the Marvelous Medicine, The Reduction Agents, and one song each from M. Ward and the Stone Roses. The sounds are supremely chill, and - in fact - one after another they create a mood that would not be out of place on a "declaring my undying love" playlist. To be blunt, they're seriously romantic songs paired most uncomfortably with seriously unromantic situations. Sometimes this effect is cringe-worthy, like the refrain from "The Pool" by The Reduction Agents: "Perhaps you intend to kiss" repeated while my brain forces me to relive that first most awful kiss of the Eagle and the Shark. Oh god, that is painful! Sometimes the effect is more cute, like "This Is the One" by the Stones Roses playing as I remember that much more cute (and only slightly less awkward) situation where Jarrod (Eagle) and Lily (Shark) are sitting together and talking. There's a line from Lily that always makes me smile because it highlights the redemptive power of even the most awkward love:
"I have two things to say. 1) I'm leaving tomorrow. 2) That could change."
With that I'll need to finish my post, but just know that the movie is worth watching (because it's uncomfortably true) and the music can be heartbreaking, or it can be heartmending. It all depends on how you listen.