My favorite version so far has been, "it's an attempt to make The Sims accessible for hardcore gamers."
The argument is that social simulations like The Sims and Prom Week are actually really complicated systems, more complicated than most supposedly "hardcore" games -- like, I tried playing Prom Week again the other day, and couldn't understand how to achieve anything because each character has a dozen abilities and a dozen moods and a dozen relationships. It seemed like a brute force approach to simulation, to dissect the gamut of human feeling and then to directly design and represent each facet. Don't even get me started on how much stuff is in The Sims... it's all very fascinating, but it's also really intimidating.
But take something like XCOM -- I really like how there are just 3 core verbs (move, shoot, overwatch) that produce a variety of situations. However, the player stories consist mostly of "my squad was in danger and we survived" or "we got massacred" or stuff along those lines. I don't think XCOM's relatively limited range of emergent narratives come from its limited verb set; I think they come from the premise of its simulation, a military squad battling aliens. What if we replaced that premise with, uh, the mundane but thrilling dramas of everyday life?
"My bros were in danger but one chatted up a really hot girl, but then she started talking about particle physics which he knew nothing about, so I had him text his friend about particle physics so he could talk to her instead. Turns out, they both hated plaid."
Other elevator pitches:
- "It's like XCOM plus Jersey Shore."
- "It's about applied linguistics and binge drinking."
- "It's like XCOM plus Love Actually."