Note: I'm talking about earphones/earbuds exclusively, headphones are fine for obvious reasons. Also some types of earphones (designed for sports) that have "ear-hooks" behind the ear are fine since the hooks will keep them in place.
Note 2: my ears don't have the "bump" (not sure what the scientific term is) that is circled in red in this picture https://imgur.com/a/CJv20Zu
Edit: that bump that I don't have is called "Antitragus" https://elementsofmorphology.nih.gov/anatomy-ear.shtml