Asteroid 2018 NW has a diameter of around 16 meters, which is around as much as 100 hot dogs. But hold onto your buns because it isn't going to hit us – though it may fly close.
I think it came from the headlines in a few articles that would say things like an asteroid the size of a car… and an asteroid the size of an elephant and two giraffes.
I think after a while it became an accepted meme to just report the size of the asteroid by comparing it to something random instead of just posting the metric size.