From Jesse Singal, http://nymag.com/scienceofus/2015/04/how-will-the-apple-watch-change-manners.html:

There’s nothing new about new technology rejiggering society’s views of what is and isn’t rude. “Technological innovations tend to have an impact on manners, obviously in part by moving the boundaries of what we consider acceptable, but also by creating new departments of manners — new things to have manners about.”

The same people that are ok with checking their phones while having a conversation with someone will also be perfectly happy tapping on their Apple Watch in the same setting. At least it will be subtler playing a game like Berry Quest on the Apple Watch instead of on an iPhone.