>>453527People are going to smoke weed on the trail. It is going to happen a lot, you are going to encounter it regularly. That being said, most (definitely not all) hikers are respecful about it. If I didn't know someone and I was going to smoke I'd always ask them if they minded, and on the rare chance that they did I'd just walk a bit away usually.
Nice thing about the AT or any trail is if you don't like someone you can just walk away from them.