My family has a similar story. My great aunt kept her salt in the sugar shaker for some odd reason, so when my mom made a cup of coffee for my grandpa at great aunt's house, mom dumped in his usual portion of "sugar" from the shaker. Grandpa took a big gulp, spat it out, and (jokingly) accused my mom of trying to poison him. They went back to the kitchen and figured out that it was salt in the shaker.

He also quietly never let her make him a cup of coffee again for the rest of his life.