If a double-decker bus crashes into (audio) a curb, it gets stuck. (We realize it didn't actually "crash" into the curb, but we'll go to great lengths to make a Smiths reference.)
Friend of SFist, Daniel, spotted this tomato red behemoth yesterday evening unsuccessfully turning left from Geary onto Stockton, in the heart of Union Square. There don't appear to be any passengers on the vehicle, or the additional weight might have caused further issues. Good thing it wasn't on a hill!