I think it is important to practice polite earbud use when in public. This entails the following rules:

1. Immediately remove earbuds when talking to anybody, at any time. Ideally remove both earbuds, but at least one. They must see you remove the earbud for this to count. If you have just one earbud in, that doesn't convey that you removed an earbud to talk to them.
2. Remove earbuds upon entering into any store or shop.
3. Intentionally insert earbuds, when eating food, only after all food has arrived and most waiter/waitress interaction is complete.

In-particular, I think transparency mode on most earbuds is socially too uncomfortable and unknown as to whether or not it's on.

Removing earbuds is not just about improving your ability to hear others – it's about signalling that you actually want to hear what others have to say and you are actively listening.

As a good example, even if I'm leaving a store, I temporarily remove my earbuds just to say thankyou to staff as I'm leaving, and put them back on when I'm outside.