You don't even need toothpaste. Taste is also a state of mind thing.

Bet a friend/family member that they can’t taste the difference between whole/2%/1%/skim milk, or some combination thereof. Blindfold them and have them begin tasting the milks. Now, replace the last milk with orange juice. The brain prepares the body for milk, and the unexpected acidity usually causes a gag reflex, and sometimes vomiting. Keep a bucket handy:

https://www.youtube.com/watch?v=FlhfIN_qbEk

I stopped drinking OJ as a teen after a decent run (4mi) and coming back super thirsty and drinking OJ just caused my mouth to keep salivating continuously (painfully) for minutes.

I vowed that day to stop drinking OJ and stick to water.

Bread isn't particularly sweet compared to other foods. Orange juice has a strange and very strong flavor compared to other juices and has a significant bitter component to its taste due to crushing the peels.

Never tried chocolate after brushing my teeth but I don't find 99% / unsweetened dark chocolate particularly offensive.

Hmmm good point maybe it's the bitterness profile of the peel

It's not. Many things taste awful, including other kinds of juices.

Wild guess: the acid amplifies whatever effect in some way.

So I thought so, but I've tried grapefruit juice, and I don't get the effect. And I can clearly taste sugar after toothpaste