Pah - sell by/use by dates!
A mate had a barbecue for his 40th birthday. I wanted some mustard for my veggie burgers and he told me there was some in his kitchen cupboard. I went into the kitchen which was a bit gloomy in the fading evening light, but didn't bother switching the light on. I spread mustard on my burgers, bit into them and promptly spat the whole lot out again. They tasted absolutely
disgusting!
I switched the light on and examined the mustard, which turned out to be orange rather than bright yellow. The use by date was many YEARS earlier, and the jar had already been opened. I asked my mate and it turned out that he didn't like mustard - it had been brought over from his gran's kitchen after she'd died nearly a decade before the party!