Could it be bad black olive that I've eaten?
Olives are naturally bitter and often fermented in brine to give a salty flavour - so they should taste bitter and salty. 

American black ("California") olives are not fermented, which is why they taste milder. If you've never had European (fermented) olives then you'll notice a bit of a kick. It may be that you've never had non-fermented olives and the flavour was just new to you. Olives are an acquired taste.

Also, given that olives are either preserved in brine or fermented they're not likely to go bad for many years. They should keep at least a year, unrefigerated.

Read more about the fermenting process here.