How to inadvertently annoy a cranky co-worker...

...especially when you are unaware of her crankiness or the level thereof.

1.  Make a random, non-critical observation about a projector screen the person is using.
2. Take off your dressy sandals because they gave you blisters.
3. Make a smart-*ss comment when she condescendingly says "there you go" to your putting on the ugly flip-flops you wore for the drive and walk to work.

Okay.  So that last one is not so inadvertent.  I'm sorry, but what woman likes having someone all but say her feet are "gross"?  Not this one!  (P.S. We're not talking big ugly blisters here.  Little ones you'd only notice if you looked for them...and you wouldn't see them from all the way down the hall!)
"If you can't be kind, at least have the decency to be vague."  I don't think she's read that quote.  I also don't care what has her panties in a bunch.  There's no excuse for being rude and snippy at your co-workers.

There.  I've vented.  Now I can clock back in from lunch and go about my day.  :-p