Nowadays, when there's a free-kick, referees spray down a magical substance that marks where the ball must be placed, that then disappears after the kick is taken. Davis Luiz, evidently, does not approve of the use of this spray. When PSG were awarded a kick against Chelsea, Luiz wiped the vanishing spray off the pitch and tried to wipe it back on at a spot he and Zlatan deemed more worthy of the kick. This is one of the more ridiculous (and by ridiculous we mean stupid) gestures of gamesmanship we have seen in a while.
Oh well, we got a chuckle out of it, and David Luiz probably did too.