Then what do you expect Cena to do? insult the crowd because they boo him? If he did that, he'll no longer be face. He's just doing his job like any other face.
No, he should adapt his character so that he can effectively function as a face. Cena is fully aware that more than 50% of the crowd boo him, he has acknowledged it for years, and the fact that he continues to do nothing about it and just spouts the same old crap despite being aware that the people are sick of it is inexcusable.