big deal or no?

How do you guys deal with a passive-agressive, irritating co-worker?

Ok...most of the people at my new job are great, but there's one person (yep, that one person, AGAIN) who is getting on my nerves. Maybe I just need to ignore her; but she constantly is asking me to do things for her and then changing her mind. (Getting her kitchen supplies, reserving conference rooms THEN CHANGING HER MIND MIDSENTENCE) She's not even my supervisor - she's my co-worker. But she seems to excel at trying to make me feel like I'm not doing a good job. Like today, she stated, "Could I borrow a pen? We don't seem to have any." Ok...

a) I use (hang on to your pants kids) ONE pen - yes, with all the economic cutbacks this year, I've decided to try to stick to one pen as long as possible. I use this pen for everything. I'm not that person in the office that has six pens lying around.
b) we DO have pens. I bought an entire two boxes. They are on the supply shelf. As I got up to show her where the pens were on the supply shelf, she blew me off and went to her OWN desk to get her OWN pen.

I don't get this fucking entitlement that people seem to have when it comes to office supplies. And I certainly don't like having to be at anyone's beck and call when they're too lazy to look for supplies and then be blown off when they decide they're too good for me to show them where they actually are.

Sometimes it feels as if some people aren't happy unless they are trying to control other people.

And this feels like a no-win situation. Small, stupid and petty, but still ANNOYING.