As language, culture and good manners go hand in hand, here you have sentences we should never say:
You are wrong is one of the most arrogant sentences you can sling at someone. Está usted equivocado is heard in Spanish all the time, unfortunately.
You don't understand is very offensive. No me entiende usted implies that the listener has a small brain capacity.
Because I say so or porque lo digo yo, shows lack of humility, arrogance again, and disrespect for the opinions of others and their freedom of thought.
I do not agree should not be uttered lightly. It is normally taken as a refutation of what has been stated. In Spanish people say this sentence all the time: No estoy de acuerdo. Better say I agree but...
What? Shouted at someone who has just spoken shows lack of respect and poor manners. Say insted: Pardon me! I'm sorry I did not catch that... or a similar sentence.
Excuses like: I have no time, I am tired, I am very busy, the traffic... are not acceptable now. We all have 24 hours a day, traffic is always terrible, everywhere, and everybody is busy... who isn't? Do you picture President Obama saying at a Press Conference: "Sorry, but today I am very tired, I have just returned from China..."?
It 's your fault, es culpa tuya, is probably right but do not say it, give others the opportunity of admiting their fault.