Why does vinegar make nail polish stick?
I thought this was sort of an internet myth, but I recently tried it (using exactly the same nail products I've used for years). I wiped my nails with apple cider vinegar and let it dry, then applied base coat, two coats of polish, and top coat. Usually, I get 6-7 days wear out of a manicure. But it's been 11 days, and while my nails aren't 100% perfect, they're certainly fine for work. I put an additional layer of top coat on a couple of days ago, once again wiping with vinegar before applying. (I always do this at least once during the life of a manicure, but without vinegar.)
I'd read on the internet that this works because the vinegar removes any extra oils from nails. However, I have long used either acetone or rubbing alcohol before applying polish as a dehydrator/oil remover, so I doubt that's it. I suspect it has something to do with pH... Maybe the vinegar roughs up the nail surface slightly?