It is a moral and societal custom, not a legal requirement. It is similar to holding a door open for someone following you into a building. Sure, it is "optional" in the legal sense to hold the door, but you look like an ass if you intentionally close the door on someone.
Still optional. You're just wasting your breath at this point. Sure it may make you look like an asshole if you don't tip. Still doesn't change the fact it's optional.
A custom is not obligated to be withheld, they are also optional.
It is a moral and societal custom, not a legal requirement. It is similar to holding a door open for someone following you into a building. Sure, it is "optional" in the legal sense to hold the door, but you look like an ass if you intentionally close the door on someone.
Still optional. You're just wasting your breath at this point. Sure it may make you look like an asshole if you don't tip. Still doesn't change the fact it's optional.
A custom is not obligated to be withheld, they are also optional.