How should a boyfriend be kindly reminded to pout when eating?

You can't stand your boyfriend eating. I don't think it's necessary to be too tactful at all. Just tell him. After all, being together is not a day or two, but probably a lifetime. Just tell him that if he cares about you, he will definitely change. It is natural and not difficult for boys to make some changes for their girlfriends. So don't think so complicated, just say it!