Technically, he was not booked for the showboating but for arguing/defending himself. Nevertheless, it was idiotic from the referee IMHO - also let Montpellier chop him down repeatedly and did precious little to discourage those tactics (particularly in terms of bookings). They went down to 9 men in the end but were called for the same number of fouls and generally did little to prevent the match into degenerating into a joke
Typically, Neymar has resorted to this bit of skill to humiliate opponents that have been kicking him repeatedly - refs can't manage the game, I have no issue with it
He's a level above everyone not named Messi but has not played a full season in 4 years - caveat emptor. Shame really, who knows what kind of player he could've been had he had the sort of professionalism of CR or Leo