The word 'glutton' often implies disapproval and is usually considered negative. Calling someone a glutton may offend them; it's not just a comment on appetite.
Pro Tip 2/3
Excess and Habit
'Glutton' suggests habitual excess, not just a one-time overindulgence. Unable to resist, the glutton often overeaten at every meal.
Pro Tip 3/3
Colloquial Usage
While formal, 'glutton' appears in casual conversation and idioms like 'glutton for punishment'. Despite the sore muscles, he's a glutton for punishment and keeps doing extra workouts.