Although, actually:

I have a related food squick which is nearly spinal, which is using personal cutlery which has already been used on a communal condiment. Like buttering one's toast, and then reaching back for more butter with the same knife.

I know it's because my mom's a celiac, and we were trained early on to never ever get crumbs in things, but it's somehow ended up this huge squick of mine that has nothing to do with whether or not there's a celiac at the table.