An easy one;
When talking to someone, stare right at their chin, or the very top of their head. We did an experiment and found that the chin stare is more annoying, because you seem to be more in the persons space.
Get into an elevator and don’t turn around to face the door. This requires nerves of steel.
We used to go into buildings and unscrew the “up/down” button panels for elevators and flip them around before reattaching them. We would also flip the “up / down” indicator lights over the doors. The consequences get pretty complicated, but ultimately leads to a lot of confused / annoyed people who step in expecting to go down and end up on the top floor. This works best in a building with glass elevators. Just pull up a chair and watch people lose it.
Of course, this is probably violating some laws and I would never condone it, except on college campuses.