"When I used to work in a shop, part of my job was to approach customers and help them out. When I used to ask people if they were OK or needed a hand I was very polite and well mannered, sometimes people were so rude and would either say a simple "no" or plain and simply ignore you. Lovely. And to be honest it really pissed me off!
Likewise if someone asked me to get them something and I went out of my way to get it and they wouldn't even give me a basic thankyou, I would fume. I just think it's really not hard to say please and thankyou, it's soo rude it did actually make a difference to me if people would forget or purposefully ignore the use of good manners"