You mustn't touch

I know I have a number of somewhat silly hang-ups about things. One of them is personal space, and another is eating in the company of others. I may have noted in a previous post that I experience some displeasure and discomfort in others nosing in on whatever I'm eating. Sure, at home I wouldn't mind my fiance grabbing a bite off my plate or touching my food, we're cool like that - but with coworkers that feels like a boundary that just shouldn't be crossed. With one of my coworkers, I can blame this on two things: she happens to have a very inquisitive nature (she's usually interrupting you to ask another question while you're trying to answer the first one) and she never wears her damn glasses. So, say I bring something from a fast food place for lunch. Even if she's got something of her own, this is usually what happens:
Co: What'd you get?
Me: Oh, just a chicken sandwich off the dollar menu (shrugging as to promote the idea it's nothing to be too interested in.)
Co: Ohh. I haven't had that before, what kind?
Me: Just a fri-
Co: Lemme see it (rolls chair over to my desk, leans in about 3 inches from sandwich)
Me: (Feeling awkward) Yep, just yer basic chicken sand-
Co: Lemme see how much meat they put on it, what else is on it? (squinting and reaching for it)
Which mostly likely will lead to me slapping her hand away and yelling "Dude, back off! I am not lifting my buns up to show you my meat!" loud enough for everyone in the office to hear.
That'll teach her.