14 yo walks into house with me after school. I go into living room and say loudly ‘hello’ to another household member who is in the living room. Teenager is in hall way at this point hanging up his bag etc.
Teen walks upstairs to get changed for an afterschool activity and doesn’t pop his head around the door to say hello.
Teen has a habit of not acknowledging people - even when he walks right past them and it is something that has been drummed into him that it is basic politeness to say hello if you pass someone for the first time that day, or when you get back, or if you go into a room and they’re there.
YABU - it’s rude and unacceptable not to pop head in to say hello when it’s clear someone’s in there as I’m talking to them.
YANBU - it’s not rude since he wasn’t in the room and was distracted with what he was doing.