For much of my life I would have proposed Elgar's Enigma Variations; specificall Nimrod. This is because every day at school for three years this was played as we marched into assembly. I was utterly sick of it, as well as finding school assemblies to be utterly miserable affairs, so there was that pavlovian association too. I once went to a play Death and the Maiden, which is about a victim of torture in South America forever associating Schubert's Death and the Maiden with her ordeal since her interogators played it whilst she was being tortured and the parallel did occur to me.
Over 40 years later I can now bear listening to it and generally quite like Elgar, but there is still that memory