I've only seen a few times where a problem has arised is where a person is just fumbling around in front of the xray so other people move up to go past. The person fumbling around seems as if they feel threatened that someone is about to go through before them and they push all their stuff up to the front and hog the space so that no one can put their stuff in.

It just makes the person seem like a jerk when there are people behind them all ready to go and the person doesn't want anyone else to get through the line before him even when he is fumbling around the inside of his bag.