I've had too many (fifteen!) arguments in the past month that went like this:
Proponent: *advocates something with no clear clue of what it is*
Me: *knows what it is, knows it's a waste of time, opposes and points out more common beliefs that are problem*
Proponent and me: *insert endless hours...
Cyclists. If you want me to treat you as a human being and not a speed bump, then obey the friggin' traffic laws. My car is not going to magically come to a complete stop within an inch just because you couldn't be bothered to obey a red light or stop sign.
Someone at work being offended because I am blunt and to the point a lot when at work. All I did was answer their question and give them the information I had (which, admittedly, wasn't any information at all).