Pato: “I don’t know what happened. I did a nice trick with the ball and they got angry. We won and played a great game.”
Simone Vergassola (Siena): “Pato did this gesture with his hands, waving us on to try and get the ball off him. That didn’t seem very professional to me.”
I didn't quite see Pato does the gesture anywhere, at the end or during the match. But, even though he did that, I believe, there's nothing wrong with it.
Just like managers like to use words for mind game, or what Materazzi did to Zidane, Pato uses gestures. This may prove important for the result of the game. The bad thing is that it may affect image and personal relationships.
Whatever it was, I think, Pato is just enjoying himself. Teenager with ability to make experienced players look like amateurs. Pato might do the gesture unconsciously because it's fun. He's just a teenager like the rush, I believe that's still normal thing to do considering his abilities and personal situations.
And Pato may lack this "hard working" or serious attitude. Because Pato didn't have to train hard for years like the others, ie: Cristiano Ronaldo, Messi, etc. to be playing for big clubs and scoring goals.
Anyway, those are just my 2 cents.
I hope Pato the best and he will develop into Milan player that can create many great records.