Originally Posted by WillCAD

I don't give a rat's posterior where anybody sits on the plane, regardless of age. It's all about behavior; well behaved children and adults are equally welcome to sit next to me, regardless of which cabin I might occupy. Badly behaved children and adults are most UNwelcome to sit anywhere near me.

Bad behavior comes in four main flavors for both children and adults, including:

* Noisy mostly this is the obnoxious business person on a cell phone, followed by the obnoxious conference goers who have to come talk over the person in the aisle seat for what seems to be eternity.. this dwarfs the amount of times a chid's noise has bothered me
* Smelly usually this is a female who happened (I presume) to spill a quart bottle of cheap perfume on her and didn't bother to change followed by some 20 something granola type just off the mountains, bike trip etc who just made it to the plane and is till picking bark out of their hair-now I know some hate certain foods but that as never bothered me so I don't count it as a "smelly" problem
* Physically Intrusive 99.9999% of the time this is a fat adult, usually male but by no means is that a given; matter of fact this is the only intrusion I've ever experienced
* Health and/or Safety Risk the only issue I know of is the one time I was in the exit row and this one guy had no clue what the FA was saying in English.. he stayed in his exit row seat though, but he never spoke a word of English and when the FA asked if he understood, he just stared at her, turned around to someone he knew and asked them something (not in English) and then the FA got acknowledgements from all but him and just let him stay.. AA Eagle for the record

Whether a particular behavior fits one of these flavors is a matter of opinion, and the opinions can be pretty polarized (witness the ongoing, never-ending argument over reclining seats).

But generally:

* If you make noise that can be heard from more than 2 rows away, I consider you noisy.

* If you can be smelled from more than 1 seat away, I consider you smelly (I have a lower tolerance for some types of smellies, as I have rather severe allergies and get shooting pains in my head from almost all perfumes and colognes in the world).

* If you or any of your belongings intrude over or under the armrest or seatback into my seat, or if you continuously impact my seat (or me) such that the impact is translated to my body, or if you impact my belongings in the overhead or under the seat in front of me, I consider you physically intrusive.

* If you bring contagious disease aboard, I consider you a health risk. And if you become intoxicated or otherwise impaired, or attempt to lift a bag that is too heavy for you above my head, or engage in other behavior which might tend to put other people at risk of physical injury or damage to their belongings, I consider you to be a safety risk.

Those are just the basics, of course; everyone evaluates the behavior of others in their own fashion.