With Barca already lead all the way through the match, Messi shouldn't do this stupid thing. It's not everyday we see Messi dive in La liga, since he use to be dominant on the match. While last night, not only Messi failed to score, but he didn't show great contribution on the match.
Not able to score, he started to dive, but with a very poor act. After he got fall by Carvalho nice challenge, Messi being told by Carvalho to stand up quickly. Messi, got up and approached Carvalho,who were just walking and leaving him, and deliberately touch his face to Carvalho's elbow. And suddenly, pretend to fall.
But the ref was clever enough to see that messi was just going nowhere, and he booked Messi with a yellow card for provoking the ref.