Siman 515

(72.) He warned against eating in a gulping, hasty manner in the way of a glutton — for this is the aspect of [Genesis 25]: "Pour into me now." Rather one should accustom oneself to eat calmly, with settled mind, and with proper conduct — in the manner that one eats with proper conduct when an important person sits at the table. So one should always eat — even when eating alone.