Somehow I forgot people who talk on those Bluetooth headsets. How did I forget that? I must have been dead at the time.

"So you were going to pick up my laundry?"
"Excuse me?"
[Very indignant with hand guestures like you killed their mother]"I'm on the phone!"
"Well pardon me for thinking you're talking to me when you're looking right at me and I see no phone in your hand."

And what makes it even worse is when you're having a conversation with them and they're wearing the headset. You can't hear the phone ring. You don't know when the conversation switches to being with you and the person to being the phone call. But yet, these people always get so pissed that you're interrupting them on the phone.

Well, here's what I say:
"Quit talking on the phone in public. That would solve all the problems. Especially if you're not going to make it very clear you're on the phone."

Seriously. I wish those things were never invented. Would it have been too much to ask the inventor to make them ring out loud so I know when a phone conversation starts? This would eliminate about half of the annoying experiences.

On second thought, this is off topic. This isn't so much a pet peeve as a major, psychotic, smurfing hatred. So, nevermind.

EDIT: I'm sorry, NeoTifa. I thought you were talking about people who actually were depressed. When I'm sitting there in an existential state thinking about who I am, what I am, and why I am, and people try to ask me what's wrong or why I'm sad, I get up and leave. I don't really want to talk about it most of the time. There are a few I do, but not like what you're saying. But then, this is going to become a whole nother thread, so, I'll stop now.