I understand if they ask you for something smaller,but refusing you service isnt on.not that many people pay with 20s. Especially since most passengers have snapper now anyway.
A few weeks back I saw a bus driver getting pissed off at someone for trying to pay with a $20. So when he saw me next in line, brandishing a $10, he got a bit upset with me as well. Started telling me off before I could even inform him as to my destination.
The look on his face when he realised my fare would be $9...