Yeah, it's all subjective and contextual. I don't know if I or anyone else can give an easy checklist to define what is or isn't "Karen" or entitled behavior, but having done my time in various positions in the service industry, it's certainly something I can know when I see it.

If I had to try I'd say it's when you have a problem and you try to resolve it in a way that gets you the most personal benefit and hormone rush instead of just getting the problem solved in an efficient manner, that's Karen behavior. Like if you order a sandwich with no tomatoes and it comes with tomatoes on it; if you call over the waiter, describe the problem in a normal tone of voice without assigning blame, and ask for a replacement, that's fine. If you use a tone of voice loud enough that other tables can hear, blame the server or cook or even take the tomatoes personally as if "ignoring" your request was a personal attack, launch into a diatribe bout how you could have bene killed if you were allergic to tomatoes, demand not only a replacement sandwich but a free side or even your whole order for free, etc, that's Karen behavior; those sorts of actions are getting you free stuff and serotonin bumps but they're causing undue stress on the staff and other people around you, who are human and have their own limitations in terms of stress and mental health, what they can do in terms of the law or dealing with their managers, etc - and they're certainly not solving the original problem (you want a sandwich without tomatoes) any faster.