I am today (by the post of a friend on facebook) that there are two different verbs that are somewhat similar: "to lay" and "to lie" (n the sense of recline). It is hard to find anyone who uses them correctly.

I also get very annoyed by the intrusive "of" as in "off of" - the correct usage is "off".

Then there's "for free". Correct usage is "free" or "for nothing".

And "refute" when the speaker means "rebut" or "reject".