The supporter made fun of Messi's missed penalty and the Brazilian answered
Neymar had an incident with a Manchester City supporter after the match. As you can see on the images, the fan made fun of Barça, looking at Neymar, after Messi missed the penalty and just before the end of the match. When the referee whistled full time, Neymar went towards to him to tell him something. The security guards had to separate them.
Despite it can't be seen on this video, some media say that during the time Neymar was on the bench (after being replaced by Pedro), the Citizens laughed on Neymar and Alves about the defeat of Brazil vs Germany (7-1) in the World Cup.
The Brazilian media say that Neymar explained that after the match: "I was playing with him. He was insulting me and I ended up making fun of him. I can't tell you what he said to me. My mother gave me some education."