The glitch in Pokémon Yellow
A minor glitch exists in Pokémon Red, Blue, Yellow. On Cinnabar Island, if Red steps right under the Gym's door without the key, and while the spot below him is being occupied by the girl NPC, he won't be able to move, and the text "The door is locked..." will repeat indefinitely. However, after closing said text enough times, the girl will start to move, thus Red is not actually stuck.
It appears to be impossible to open the Start button menu during the moment when the text box is closed, until Red is free.