I don't remember when's the last time I tasted soap, but it's just something you don't forget.

At least in one of my chem classes we where taught bases vs acids and we definitely tasted soap then.

Also, showering.

I do. It was around 1955 when I was 7 years old. I said a bad word and my mother literally took a bar of soap and shoved it in my mouth. I still vividly recall how horrible it tasted and felt.

Ever not rinsed a glass enough after washing it?

It tastes like you didn't rinse all the dish soap out of a glass, surely you've experienced that at some point in your life, probably more often if you've ever hand washed dishes.

Ever had beer?