I witnessed an interesting event this morning when I boarded a bus. There were four people ahead of me in the line; the first two boarded without issue. The third person was in the process of paying by cash when the man behind her swiped his bus card on the scanner. When the driver had finished the transaction with the lady, he scolded the man for not waiting until the person ahead of him in the queue had finished paying.
The man's response? He complained that he was saving the driver time by swiping then rather than later. This caused the driver to give the man a lecture about being patient and waiting his turn; when the man argued back, the driver asked if he wanted to leave the bus, noting that he was "being rude". He then told the man to sit down, which the man did.
I can see the event from both sides. The man possibly acted in good faith and thought he was saving the driver a few seconds of time; after all, he did not barge past the woman ahead of him when he swiped - he waited. That being said, the driver has to oversee all transactions and it's hard for him to watch the scanner when he's dealing with someone paying by cash. There's also the matter of simple politeness - it was not yet the man's turn in the queue when he swiped.
The lesson here? Regardless of your intentions, wait for your turn in the queue.