Mayonnaise is usually reserved for sandwiches right??
Well here's something else you can do with mayonnaise.
I have had a watermark stain on my antique baby grand piano - for years...which I've just been covering up with my pile of music books. I came across an article with 35 'great tips that will change your life" and read that if you smear mayonnaise on a watermark on a piece of furniture then it will disappear! I decided it was worth a try - and to my surprise, it worked a treat.
My piano is lacquered, I don't think I'd do it on an unlacquered wood as it would just seep into the wood and make an oily stain.
And as for changing my life... I'm not looking to do that, and if I was, I think that might take more than a jar of mayonnaise!