I think the general term refers to someone who is an inexperienced, infrequent flier AND their confusion negatively impacts those around them.

I add that second part because the vast majority of people in airports are infrequent fliers, but have some basic common sense, so their inexperience doesn't interrupt the general flow.

A KETTLE however, is the sort of person who forgets to remove their jewelry at the security checkpoint or seaparate their toiletries, ending up taking 20 minutes just to get through. A Kettle doesn't grasp the concept of ordered boarding and stands in the FC line while holding a coach ticket, and then cannot find their seat because they don't realize that row 22 is behind row 21 and that one side of the plane is ABC and the other is DEF. A Kettle doesn't understand crowd flow, and likes to stop and stand confused in high foot traffic areas: The top of the jetway, the entrances to the toilets, the security exit and so forth. A Kettle thinks the flight attendant is a waitress and treats her as such. A kettle returns from the lav and steadies themselves by grabbing every aisle seat headrest on along the way. Kettles see FA's from other airlines walking through the terminal and think of them as info booths for their own flight, janitors too. Kettles impact those around them in a negative way.

Generally, Kettles fly coach. They don't earn enough for ugs. But not always. I have seen Kettles in F several times. Being in coach does not make one a kettle.

I have also seen the term used to describe the collective VOLUME of inexperienced fliers in one place. For example, gate lice and line jumpers on WN flights.

Some people find the term offensive because it reeks of classism or elitism. Particularly in the US, where we are supposed to pretend there is no such thing as class differences. I disagree personally, I think it is perfectly appropriate and we cannot deny the existence of such people. We could call them worse.