I try not to be, but I can't help it sometimes.
Example: If someone says or does something incredibly stupid I can't help but laugh at their stupidity...REALLY laugh, out loud, in their face.
I had a girls night out one night and my friend was drinking. She walked up to this woman wearing an extremely ugly outfit and gave her a "DWI" ticket. The woman asked "How can you give me a DWI when I am not driving, I am sitting in a bar". My friend told her "Hunny, that is not for drinking and driving, this DWI is for Dressing Without Instruction".
Yes, my friend was very rude, but I couldn't help myself, I laughed uncontrollably. I felt bad about it later because I didn't know if I hurt the woman's feelings or not, but it was still hilarious when it happened.
What do you do that can be considered "rude" to other people?