This will be a short post, but everyone should read this and take note.
Proper elevator etiquette states that when the elevator opens, if you’re waiting to board, you wait until everyone that is getting off at that floor gets off. As with most etiquette, this has a practical reason. If the elevator is full, you will not be able to board. Also, if you board before anyone gets off, you may block the people wanting to disembark from the elevator from doing so.
So, if you don’t wait, and you get run over by an overweight IT guy, that overweight IT guy isn’t crying for your dumb ass. Just sayin’