I'm coming in a bit late on this one, but what I can't stand is people not knowing how to use an apostrophe.
"I hate monday's".
Hate monday's what? What is it that monday owns that you hate?
"I hate monday's".
Hate monday's what? What is it that monday owns that you hate?
"It is the mark of an educated mind to be able to entertain a thought without accepting it" ~ Aristotle