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The thing about British serial killers is that they’re so polite. “Sightseers” is a low-budget lark about a homicidal couple on vacation: Chris and Tina (Steve Oram and Alice Lowe, who co-wrote the script) have been dating for a few months when they head out on holiday in an RV and realize they share a taste for murdering litterbugs, snobs, and other unpleasant people.
Darkly funny as it is, the movie has undercurrents of genuine and very British weirdness. The director is an up-and-comer named Ben Wheatley — he made the unnerving “Kill List” in 2011 — and beneath the whimsy is a class rage as heartfelt as it is warped. The movie doesn’t add up to much, but it doesn’t really need to.