There are gray areas and black & white areas. I can contemplate your differing definition and see that as understandable. However I have never known anyone, barring those in an “open” relationship, who would see WhyNot’s actions as anything other than upsetting to the SO looking on.
Indeed where is WhyNot’s responsibility in this? I certainly would say her views are at the least on the fringe of what anyone would reasonably call understandable and acceptable. Surely she has to have a clue that her definition of acceptable “flirting” is a bit more aggressive than the norm unless she wants to tell us in her world everyone she knows acts that way. We take our clues from society around us and that one is unusual everywhere I have ever seen.
Given that is it not more incumbent on WhyNot to make her partners aware of how she is a liable to act?
Further, and no one has answered this yet, I really have to wonder if WhyNot would be absolutely content and have no issue of she turned around to see her SO playing tonsil hockey with some hot blond two feet away from her.
In the end I think the Golden Rule applies well here. Don’t do what you would be upset having people do to you and if your norms are notably different from most everyone else you had better be upfront with people about them (at least those you are close to).