It's trivial but I hate it when I tell someone that I'm sorry as in..
"You hurt your back? That sucks, I'm sorry."
"Your grandmother died? Oh, I'm so sorry!"
and they respond with
"Oh that's okay, it's not your fault."
Argghh. I know that your Didi's death wasn't my fault! She lived in freakin' Mumbai!
Sometimes I'll clarify that I wasn't apologizing but offering sympathy and sometimes, like the cashier at the grocery store with the aching back, I'll just let it go.
It still peeves me though.