Why Are People So "Thirsty" at Airport Security?

People need to calm down while going through airport security.  We have all gone through the steps - we know how it goes- place your luggage on the conveyor belt, put your laptop in a bin separately from your other things, place the rest of your items (jacket, shoes, purse) in another bin and send it all through.  Patiently, I wait for the person in front of me to place all of their items in the bins and on the conveyor belt.  Ah, now it's my turn.  I take my small carry-on bag and place it on the belt.  I reach to grab a bin for my laptop and some eager passenger behind be plops his bag down.  I look at him as if to say, "What the H do you think you are doing?"  He moves his things back.  I place my laptop in the bin, reach to grab the bin for the rest of my things and "plop!" goes his bag again.  I look at him and say, "you need to calm down, buddy."  Again, he pulls his things back to allow me to finish putting my things through security.  This has happened on more than one occasion.  Are people clueless to what's going on around them? Is it that serious?  Are you going to a fire after you get through security?  What's the rush?