Mira put this sign on my office door a few weeks ago. In case you can't read 1st grade English, it says, "Do not come in. I am frustrated. But you can talk to me." She put it there when she retreated to my office for some alone time after something upset her.
I've decided to leave it up because the message pretty much applies to me on a regular basis while I'm working: I'm frustrated, but you can still talk to me. In fact, I'm sure you can relate to this message too and you should probably post a similar sign on your office door to serve as fair warning to unwitting coworkers. I like the way the note conveys one's current state of mind in a straightforward way, but also says "I'm dealing with it. I'll take your calls anyway and we'll have a civil discourse." I like it a lot.