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Well, yes...
According to several sources, the reason he did this was because he didn't accept being called a "loser." Both Enrique and Jaoa Pedro had their own reasons for this unexpected incident, as reported on the following page. You're right, however, everyone should remain calm and respect the winner. They must be able to control their passions and emotions, which can cause a commotion. And of course, no one can underestimate their opponent in every match.
Source: Luis Enrique and Joao Pedro explaining what happenedAnd because of this incident, the rumor is that Enrique will be banned for 3 matches.
Source: PSG boss Luis Enrique is facing a three-match banBut if that is the only excuse that Enrique has and that he deems valid, he should have been well advised to just shut up instead and send out an apology to everyone who saw this incident and felt insulted by it. Being called a loser when actually you are a loser in a game is no reason to freak out like Enrique did. Is it justified or good manners to call anyone a loser, if by the way thisis true? No it is not, but as someone who has won so much and who has had the privilege to beat Inter Milan 5-0 in a UCL final should hold back, take a deep breath and take those words like a champion. Enrique could have said "see you in the UCL" and give him a wink with his eyes. That would have been a valid response and he would have implied that this wasn't the last time they meet and next time it is about to be revenge time.
This was like a little insulted kid playing in the sandbox getting a shovel stolen and then going crazy.