People on the phone when the poor check out chick is just trying to do her job.
People get to the check out chick and then decide to fumble to get their purse or wallet out to pay.
Your in a hurry but the person in front of you decides to have a parley with the check out chick about any and everything but what she is buying . (its never a he )
Friends who meet in the aisle block it and carry on a coversation oblivious to anybody else trying to get past.