xkcd

What's interesting are the states you can't modify too much or it gives away the game.

Texas is a key example, people are pretty familiar with that shape, even many non-Americans will recognize it. Florida and California are also pretty well known. Also, many people have a rough idea of NY State, though you could probably tweak the north and west borders a bit and nobody would notice too much.

The ones it's easy to fiddle with are the rectangular ones in the mid-west. I think a lot of people only know them starting from another reference point, like "north of Texas" or "east of Nevada".