You might not think much of it, but small things like not sharing arm rests or helping people with their carry on bags can lead to unexpected fights among passengers or flight attendants.
Brown says a big thing that bothers her is when people take their shoes off on the plane to walk around and let's just say the odor is less than desirable. But it's not only air travel etiquette that's being violated, "One of the worst travel offenses is the people who put down their towel at the hotel pool. And then disappear 6 or 7 hours at a time. It's just not fair. If you're going to be away from your deck chair on a cruise or your beach chair or your pool chair for more than a hour you really need to pack up all of your stuff and take it away with you."
Now Brown says in some people's defense, there will be people who aren't exactly travel savvy. Meaning they only travel by plane maybe once a year or once every few years. So if you see someone that's breaking the etiquette rules, just ask nicely and tell them what's bother you and you'll be surprised how well that exchange will turn out.
One more thing to share -- when asking to change seats on a plane remember to trade only if your are offering something equal or better. For example if you have a middle seat you cannot ask someone with a window or aisle seat. But if you have a money seat and need to sit with someone and you move to the middle.