Other people's poo
Rancid oranges because they smell very similar to late stage human decomp and I can't smell the one without remembering the other.
Durians do smell unpleasant and the smell lingers. I think they taste unpleasant too.Durians.
Everyone seems to marvel at their taste, including Bill Bailey as seen in his documentary, but the horrible, headache-inducing smell puts me right off.
It smells like rotting flesh and a gas leak.
The best contraceptive known to mankind
Rotten potatoes.
These, and in this order. Worse still is when you pick a rotten potato out of a bag and your thumb/fingers squelch through the skin and the stench is transferred to your hand.Coffee breath