How about the fact there are so-called bisexuals?
Swinging whichever way the wind blows your chimes . . .
I have found that it is the so-called bisexuals that annoy gay activists the most as they try to argue homosexuality is not a behavioral choice. They generally try to avoid discussing so-called bisexuality completely for this reason. Bisexuality puts the lie to their agitprop.
Besides which, I don't define homosexuality or bisexuality as behavior. I think of it as attraction.