i'd try to explain agender first and then be like "there's a smooth gradient between all three things, like colors turning from whatever to whatever else. it's an oversimplification but boomers are simple folk.
or like, ask them what gender some asexually reproducing animal is.
At least for me, I’m aware that a guy is expected to behave in a number of ways that are deemed “masculine” and I’ve never fit into those characterizations. Only after spending some time on my own for awhile did I realize that a lot of my previous behavior was only the case because I thought it was how I should behave as someone with a dick, not how I wanted to behave. If you think about it, it’s kinda silly to categorize a human as only belonging to two different groups. Intersex people exist too!
But I’m still struggling with what other things could explain that (be it a naturally low sex drive or asexually)
I do my best to quickly differentiate sex from gender as a biology versus largely social definition and try to mention the examples of a 'third gender' across many cultures before they can reach for a shotgun and Bible.
Ma, remember when you got hired by IBM back in the 70s to punch 0s and 1s into paper cards and got paid a livable wage to buy us a house? Imagine all that, but you also punch 2s on the paper card every now and then.
"it means a person who doesnt associate with a specific binary gender aka man/woman. its kinda like a third gender." if they can't understand that it's probably not worth the time because clearly they are fucking stupid.