The Shopkeeper "Ramen Guy"
About
He (and, by extension, Ramen Darou) has five Golden Rules. They are as follows:
1. Thou shalt not speak.
2. Thou shalt immediately buy your ticket and promptly take your seat.
3. Thou shalt uphold manners, respect the shopkeeper and wait with peace of mind.
4. Thou shalt not touch your cell phone.
5. Thou shalt return your bowl once you finish eating and immediately give up your seat.
Komi, having already been shown to share Shopkeepers lack of communication skills, is also adept at following his rules, and is shown to be a model customer.
He debuts in episode 5 of the anime, and chapter 65 of the manga.
(Source: Komi-san Wiki, edited)