I got great seats up against the glass at a local hockey game and took my nephew. Partway through the game, the lady sitting next to him pulls out a bottle of nail polish remover and starts taking off the polish from her toes. My nephew told me it was giving him a headache so I switched spots with him and tried to give the lady a look but she was totally unfazed. She then pulls out bottle after bottle of nail polish from her bag. She had like 4 bottles and she lined them up on the boards, plops her feet up on the boards and starts doing her nails. I was so blown away but did not say anything. Just sat there thinking about how self centered you need to be to lack any awareness of your surroundings. She was taking her time and doing fine details and I just sat there, completely unable to focus on the game because of what was happening next to me and how out of place it seemed. So, it came as a bit of a surprise to both her and me when finally a hit came just up the boards from her knocking all four bottles, which she had not been resreweing the caps on, off the boards onto the ground and splattering nail polish all over her purse and my shoes. My nephew and I burst out laughing but she lost it. Like grown woman temper tantrum. She stormed off which was hilarious as she was also trying not to step in the nail polish or screw up her nails. After a while the guy she was with left too. Never saw them again but I'll never forget it. Seems unreal. I never grew up around girls doing their nails and it blows me away that someone would do their toenails at a restaurant, at a hockey game, or in a car. Now sometimes if I have a hockey game on TV, my wife will do her nails as a running joke.
As for getting it off your seat, there is a balance. Anything that will remove the nail polish easily is almost certainly also hard on the seat and not something you want to concentrate on one area with. If you go with something harsh, you can test in an area you don't see often first to make sure it won't stain. Often times you want to find something that that is as gentle as possible that still works with some effort. Nail polish remover or acetone would work with just a wipe or two, but it might discolor the seat too. I don't really know what would work best, but I'd probably start with a leather cleaner and see if I could get anywhere with it first.
As for punishment, I'd not let my wife live that down anytime soon. If she was going out, I'd probably indulge myself in a quick check of her purse for contraband and stuff like that. Maybe leave an article or two out about what age developmentally a kid should be able to color inside the lines. Possibly lay down plastic wrap on her seat at least a few times. Next time she was car shopping, be sure to ask the sales person how hard it is to get nail polish out of the seats with as strait a face as possible.