The female praying mantis RIPS OFF THE MALE'S HEAD during sex!
Often, the male will try to initiate courtship in secret (technically rape, but in his defense, there's a good chance he's about to become someone's lunch). If detected, the female will kill him and eat him, often by ripping off his head mid-coitus. Upon being decapitated, the male mantis will reflexively tense up and start to deliver sperm more vigorously than before. Afterwords, in lieu of a cigarette, the female mantis will relax by eating whatever is left of her new ex-boyfriend.
Most mantises don't do this, but the most famous species of mantis, Mantis Religiosa (aka the "Praying Mantis"), does this all the time, thus giving the rest of the mantis family a bad name. For some reason, male praying mantises are undeterred by this and they continue to initiate this bizarre mating ritual. The technical term for this process is "Sexual Cannibalism", a fetish that (thankfully) has yet to catch on much among humans.