I've already tried to explain why so many people hate him. I think it's because he's uniquely awful. Everything about him. He looks ridiculous and you can only get away with looking - and acting - so stupid if you're a good player. He's awful. And he's frequently violent and clumsy. And he often makes the team play unattractive football by his mere presence. And he literally doesn't even try half the time.
I think it's the unique combination of awfulness that pisses people off.
So it is irrational really, imagine people booing Lingard because he dabs and dabbing is for idiots, or booing Pogba because of his stupid hairdo. Violent, sure, more often than not you'll see crowd cheering when somebody other from our team plays it rough, pretty much nobody would mind an elbow on one of Spurs' players I can bet. The unattractive football is always questionable for me and the last one, you know it, is bullshit. When he was playing he was, alongside Mata, the man to cover the most ground for us, he was generally speaking top of ground covered in the league up until then, when we were the least running team in the league. Hardly 'not trying' half the time.
So yeah, if you think that booing him is fine because you simply don't like him, just say it instead of trying to make some ridiculous reasoning behind it in 'stupid hair' ilk, it's just silly.