Something I do find weird and annoying is when Im at a station where I know a lot of people get off so I don't bother pressing the button, especially when the button is in the centre of the doorway, because people wishing to alight who are already on the train will do that instead. Still, almost without fail someone will barge in front of me, push the button then be right in the way of everyone wishing to alight. Some even looked shocked that people alighting don't let them board first. When on the train, whether pressing the button in advance does anything or not, I do have an expectation that the first person has their hand on the button to make it clear they understand the system but when on the platform, just wait for people to alight or wait for the button to light up.
Another thing is when people smash the button. Although it's been mentioned already, i honestly wonder if people think it will make the doors open any faster. The only exception in my opinion is on Siemens Desiros because I understand the doors don't move for a second after you've pressed the button so you may be inclined to press again to check but there's still no need to smash the button to pieces.