Is this UGC? If so, the writer probably didn't even realize what he was doing. (Should have, but didn't.) Betcha he had one of those "smart quotes" options turned on. I have to type my curly quotes and apostrophes manually because the text editor isn't clever enough to leave them unaltered when-and-only-when they're inside html tags.
But if a request is reaching your site with extraneous bad characters, it should still redirect :( Or return a [G] or whatever approach you choose to take.