Kiss has been accused of lip synching their live show during a June 6 performance in Antwerp, Belgium. According to a video posted by YouTube user The Fonz, guitarist Paul Stanley's vocal track seems to play without him actually being at the mic. The misplaced vocal track is thanks to drummer Eric Singer allegedly missing a beat, making up for it by adding a bar, the pyro firing off too early, and "Paul is left with his pants down when his vocal plays without him pretending to sing it."
It's a situation where one video makes it pretty hard to tell what's going on – the vocal is pretty quiet and Stanley is near enough the microphone where maybe he could've yelled the line? Who knows, and I'm not sure it's entirely fair to accuse Stanley of lip synching when there's just one video where the volume isn't exactly the best. It's also probably worth noting that the vocal could've been a backing track used to supplement Stanley's actual sung vocal, and he was just caught off guard due to the misplaced beat. So not lip synching, but a backing track playing without the live performance over it.
Lip synching has been a weirdly hot issue this year. Dream Theater vocalist James LaBrie was accused of doing it live (much to his dismay), while Fozzy vocalist Chris Jericho took the side of backing tracks aiding artists live to fill out their sound. Radio personality Eddie Trunk also got into a public spat with the band Santa Cruz over the issue, saying "It's the norm in pop, it's gotta stop in rock."