I do it to piss them off.
I think of that as backwards. People IMO deserve basic human respect until they prove otherwise–and even then they get cool civility, because (as above) I want to be a polite person in myself. If I went around waiting for every person I met to prove to me their worth before I bothered to treat them nicely, I would make a lot of unnecessary enemies–and personally, I wouldn’t be very thrilled to be constantly met with implicit challeges to prove myself worthy of good treatment. What should we all do, type up little personal information sheets to hand out to all and sundry?
genie, you’ve got me wrong, I am respectful to everyone until they give me a reason not to be.
Respect, like trust, is mutual - if someone disrespects you respect is not just impractical but impossible. The polite attitude becomes a mask for something else.
Sometimes being overly polite is just lack of self esteem. I am one of a family who say “sorry” if someone bumps in to us! I swear not one single member of my family could complain about anything because we don’t feel we have the “right”. I have been out to dinner with my family and someone got something pretty much inedible. Not one of us could rustle up the guts to complain.
I currently have a brand new computer that is not doing what is should be but I can’t get up the balls to ring and complain.
In my family even deciding what to do on a day out is a pain in the bum. No one feels they have the "right’ to make a decision. So we all do the “What do you want to do?” “No what do you want to do?” thing. It is horrible and frustrating.
Being polite is not a good thing sometimes, but we will keep doing it. Grrrrrrrrrrrrrr.
kiwi, PLEASE do not equate wussiness with politeness. There’s plenty of people who are polite and who are still able to demand good service at restaurants (they’re the ones who manage to do it without being jerks to their servers). Being unable to make a decision isn’t polite - it’s damn irritating, in fact, and it’s a sign, as you said, of low self-esteem. Politeness is something entirely different.
True…it is just labeled as polite sometimes.
shall I say sorry now? 
> Why should I be polite to someone who doesn’t deserve it?
> Because I want to be a polite person. Whether or not the
> person deserves it is not the question; whether or not I want
> to let other people change how I behave is.
Exactly. You are descending to their level if you fly off the handle and start using insults and cussing.
I mean, you are upset at them in the first place because they did or said something you feel was improper or uncalled for, right?
They win the game if they can break your composure.