i despise that! it comes off in seconds with a scourer but if the offending cup had been washed up within an hour of use it wouldn't happen! My OH has cups like that at work and each time I go I clean them and he moans about it, but I refuse to drink coffee from such a disgusting cup. He says it adds to theflavour of the tea, how does it add to the flavour of coffee though? If all the cups have such stains, how can you make a cuppa soup? And is it true it adds to the flavour of a tetley tea bag? if that's true why don't tetley advertise that 'tetley make tea bags that make mucky cuos taste lke tea'? I know that tea leaves used to stain the inside of a tea pot and that did apparently help with the brewing process, but tea bags are inside the bag and the leaves don;t touch the inside of the cup! the idea of tanning on the inside of a teapot is that the leaves of loose tea were swirled around inside the tepot to enhamce the flavour and then it was left to settle, tea bags don't need that!