People who stand in doorways. Or stand at the top/bottom of escalators.
What's wrong with these morons? Having got into the doorway of a public building such as a shop, hospital, railway station, airport, cinema, theatre or many other things, some people, especially if there are a few of them and - usually - over 60 years old, they stand stock still preventing those immediately behind them from entering/leaving the same building. What's going through their heads? Don't they realise the inconvenience they're causing? Or, at the top/bottom of escalators, the danger they're causing to the people behind?