"Let's play D&D!"
"Cool! That's my favorite game."
"First a few house rules for my D&D game: no dragonborn or gnomes. No humans, dwarves, elves, halflings, tieflings, or tabaxi either. We don't use alignment, we don't use experience points, and we don't use armor class. Swords are called 'machetes,' magic is called 'psionics,' and there's only one character class called the Gishrogue. You won't be fighting dragons, you'll fight oozes...and you don't fight them in dungeons, you fight them in swamps. And the big one: we don't roll any dice, we resolve things by playing rock-paper-scissors-lizard-Spock. Sound good?"
"No, that does not sound good. Are you sure you're still playing D&D?"
"Of course we are! Weren't you even listening? It's literally the first thing I said!"