No earbuds fit my ears. I can wear in-ear monitors and ear hooks, but no earbuds. I've known this since my friend got his Gameboy with Tetris and stereo earbuds back in 1989. My twin brother is the exact same way. I have tried many times over the years, especially as they gradually replaced headphones, but there are no exceptions: none will stay in, even when sitting down.
I think it's ridiculous that the industry ever thought that they worked well enough for enough people to package them exclusively with nearly every personal audio device since the iPod as opposed to in-ear types. Even Apple's so-called "ear pods" that they released in 2012 fall right out (useless). If they really scanned and tested so many hundreds or thousands of ear shapes then they should know that the number of incompatible ears is too high to justify this when a functional alternative already exists: Why not just make them fit in the ear canal like in-car monitors?!