There is one big annoying "feature" in mp3 player. If you play streamed song from your server, the player can't handle multiple playlists. So tapping new song while another is playing causes new song to interrupt playback. That is frustrating for example in parties when you would like to make long playlist with mp3 player program.

Volume-button-not-working and headphone-plug-in-wrong-end are also quite annoying design flaws.