Using 'seen' instead of 'saw' irritates me to no end. I also really, really hate when people (outside of texting) use r, n, u, or the worst of all.. ur as actual words.
But speaking of regional things, when I first moved to north Florida from the midwest, it drove me absolutely NUTS to hear cashiers in stores say "...and five dollars forty two cent is your change". If there are more than one of them, that makes it plural. It's centS. No matter the denomination of the change, it was always 'cent'.