In discussing the pilot, there was a future plot point I thought was telegraphed so heavily it won't be an effective revelation. My friend disputed this analysis, suggesting I must have contracted some sort of brain parasite to have thought of such a stupid idea. Spoilers from the pilot.
There are a couple of flashbacks and references to an unhinged Kevin running around naked, having had some sort of supreme meltdown at the time of the disappearances.*
At the end, when the woman in the bar asks him what he was doing when everybody disappeared, there's a flashback to an episode of sexual intercourse well underway.
It seemed obvious to me that Kevin's partner in coitus vanished right there during the act, prompting him to lose exactly all of his shit.
Solid Leftovers Theory or Moronic Blather?
*This scenario fails to account for the blood splattered on Kevin during his al fresco adventure.