There are so many inconsequential things that piss me off that I know that I am the problem.
I will boil it all down to the inability of a large segement of the population to think ahead.
Everyone pulling up to the 4 way stop should know the order. They just saw it all form before their eyes. Usually it is someone on a cell phone screwing it all up.
After standing in the coffee shop line for 10 minutes, mommy takes her turn to read the board and start discussing what snotty-nosed junior wants from the menu. How about discussing this "before" it is your turn to order. Same goes for a drive thru.
Drivers who don't look down the road to anticipate things, thus slamming on brakes and doing other things to slow up everyone.
The family with the stroller, dog, and 3 kids who wait until you must stop walking or running to negotiate their madness before they even notice anyone else is coming.
Waiting until the last moment to get out your credit card or cash to pay for something. Of course this person can't decide or find their method of payment.
Think ahead a little people. I could go on for ever.