Why do small things annoy us so much?

I’ve noticed at work (I’m a cashier at wawa) that the following things bug me:
Bagging things that dont need to be bagged
bagging newspapers
being told someone doesnt need a bag . . .when its obvious ( like for a cup of coffee)
Having people put money on the counter instead of my open hand
Holding money up in my face till I take it
Ask for matches before I offer them
Pay with 100 dollar bills
Act like Im wasting their time
The list goes on and on I actually plan to mark off how many times I get annoyed at work tomorrow. My question is why would small unimportant things . . . such as bag politics annoy people? Well maybe the bag thing is just me but you get my point