My real exception is when someone is unkind or rude to me or someone else. I don't hesitate to say something like, "Civliity is not your strong suit, is it?"

I'm polite until someone gives me reason not to be.

I don't think not saying thank you or whatever when you are getting on or off the bus is too big a deal. You're taking them to where they don't want to go and possibly where they get bullied every day. Also, they could just be in a bad mood, so I don't think its too big of an issue. I always say please and thank you and greet whoever serves me, but if someone doesn't respond or whatever I just assume they're in a bad mood and don't really feel like talking. Which I totally get.

I think it is good to be polite. However, I do not think disrespectful actions should be indulged with a polite response. I would not make a good public servant. I teach kids the same thing, if an adult disrespects you without cause, feel free to disregard their commands, authority or opinions. If you need another adult to get in their face about it, come find me.

Not only do I try to be polite with everyone, but I also put on a smile; regardless of whatever kind of day I'm having. There's no point in compounding my or anyone else's 'issues' by being grumpy or negative.
Oh, and were applicable (like at my morning drive-through), I also remove my sunglasses when talking with anyone (like the servers).

I agree with you 100%.

Doesn't cost a thing, feels good for both you and the other guy. It's a two way street though. If the other guy is a dick, I change my strategy a bit.

I am polite until you are not! You get what you earn!

I taught my kids the same as well

It's really important to me to be polite to everyone.

It’s not so much that I’m not polite, it’s just that I’m blunt and up front. Which people mistake for rudeness. But, if I like you and have known you for a while, I’m more likely to sugarcoat things a bit more.

Must admit, I don't always make it 100% of the time, to my shame.