Six friends, Anton, Bradley, Carlton, Devon, Ellis, and Frank, go out to eat together at an all-night diner. At the end of the meal they're presented with a dessert menu, upon which is listed two options: peach ice cream, or pistachio ice cream.
"Dude!" says Anton, "I love peach ice cream! It's my favorite. But man, pistachio is not for me. If they're out of peach I'm just going to have to go to bed without dessert, because I'm not having anything but peach."
"Wow, really?" says Bradley. "That's so crazy- I'm the exact opposite! I love pistachio ice cream! It's all I ever want. And you couldn't pay me to eat peach."
"You guys are insane," says Carlton."Ice cream is ice cream, and you're crazy to turn down any sort. I mean yeah, I prefer peach, but no way am I going to say no to pistachio, if that's all they have on hand. What about you, Devon?"
Devon shrugs. "Eh, I don't really have a preference. I'll have whichever's easiest to get."
Ellis politely hands the menu back. "I don't do dessert."
"I wonder," says Frank with a grin for the waitress, "if I could possibly get a double-scoop?"
And that, my friends, is how I used ice-cream preference to explain the spectrum of sexuality to a friend who didn't understand how a bisexual man is not gay. I'm pretty sure he gets it now.