- Fields with super strict validation. For example, if you typed a postal code and "V5X4O4" works but "V5X 4O4" doesn't.

 - Icons with no textual label or title (on hover or not).

 - If a title is being truncated, I think you should be able to see a tooltip with the full title on hover.

 - When important buttons are obfuscated from end users in favour of advertisements or promotional material. Think of PayPal's "Continue without an account" button.

- AUDIO THAT PLAYS WITHOUT PERMISSION! Lol - Also, no mute button.