Not that he should care about it, and he probably doesn't, but a lot of neutral football fans all around the world, who only ever get to see Gigi when he plays for the NT or with Juve in the CL, will remember him for this outburst imo.
Not that there aren't plenty of great things/epic moments to remember him for, but it happened at the end if his career, there isn't much more to come, and people do have short memories. Not to mention it was just so unusual for him to act like that. He's always only spoken about others with respect, Journos and players alike who looked up to him and cocksucked him whenever given the oportunity to do so, naming him as the perfect role model and so on, now see him exposed as salty, bad loser (not my opinion, just reading what has been written on websites over the past few days).
He didn't headbutt another player, but given the timing, and most importantly how unusual it was for him to act like that made it worse than it actually was. If it was any other player, i'd say who gives a fuck? But Gigi was/is the ultimate nice guy in football, not anymore. It's a sour taste that will stay imo.
It's obviously gonna change nothing for Juve fans, for whom he's won tons of trophies for, bleeding the club colours for decades now, but imo it might very well change how the neutral looks at him.