Interrupting the end-of-summer plainness like an ice bucket over the head is The Guest, a fun, nasty little slice of nuclear family devastation. It’s a tight, black domestic thriller from the seasoned horror partnership of Adam Winberg and Simon Barrett. Like the duo’s previous film, the rudimentary but spirited slasher You’re Next, it’s a genre piece about home invasion and family dysfunction. Here the threat isn’t a gang of animal-mask mercenaries, but a wolf in ship’s clothing. If the sheep shopped at Abercrombie and Finch. The Peterson family, still reeling from the death of son/brother Caleb in the Afghanistan conflict,…