I couldnt resist..........Wife was moaning about a rust mark down the sink caused with a few drips over a couple of years when the tap was turned off which hit the overflow outlet.
So told her to google it as she cant afford to pay for my knowledge :-) She tried lemon juice /salt/bicarbonate of soda/bleach/vinegar and everthing in between nothing removed it.
Knowing one way or the other I would remove the stain I told her when I have a couple of minutes to spare I will sort it, she went shopping so used toothpaste and and wiped the stains off in seconds!
She wasnt impressed as she now thinks I am a c... for letting her slave over it for days.