I don't have adult grandchildren yet, but if I did, love them or not, I would probably avoid any further contact if they ever spoke to me like that in the scenario that the OP has described. The same goes for my adult children if they were to do it.
Any typical 23 year old is old enough to know what is unacceptable, and also how there are different standards for different generations. If someone has always treated them with respect, they should know never speak to them like that!
My own sons can be very rude to their father, my OH, but that is because he speaks to them like that too.
I would be very upset if they spoke to me the same way, but they never have, because I have never spoken to them in that way. They have always realized that it would be very wrong to speak to most people like that.
Times might be changing, but I would still expect the OP's grandson to 'know' and apply such social rules at his age.
I would like to think that if that had happened to me, I would have told him (afterwards perhaps if it was a group situation), in no uncertain terms, that it was totally unacceptable. However, as I hate confrontation, I would not find it easy.