For me it is a mixture of “you” and “I”, with “you” being more prevalent.
“Your Excellency.” So, second-person singular, I guess.
Hey, did she just call you crazy? I think she did. No, she said she *thought *only crazy people talked to themselves in mirrors; she could be acknowledging that this previously held information is wrong. Yeah, do you think that’s it? So what if she thinks you’re crazy. Yeah, I’m not crazy. I’m sure other people talk to themselves, too. Hey, how do you know she’s a she? I dunno, that’s just the gender I assigned for some reason. Oh, okay. Cool.
I don’t think I’ve ever talked to myself in a mirror. I have exclaimed things like, “Oh my god I look like shit today!” but that’s just saying stuff out loud.
Not that I don’t talk to myself. Just don’t spend much time in front of mirrors is all.
I don’t either.
Just so we’re clear, I don’t get all “Taxi Driver” with it, but I tend to groom in front of the mirror, and typically I make commentary to myself on how I’m doing.
Oh yeah, there’s the cats to bounce things off of. And sometimes I run ideas past them, too! {rimshot} 
I voted second person, but I don’t very often talk out loud to myself, in the mirror or otherwise. It’s an internal dialogue unless I’m very pissed off and haranguing myself. Even if I actually think I look good (which is sadly rare), I don’t tell me so out loud.
nope, I don’t
I can’t recall ever talking to myself in a mirror specifically, but I do talk to myself all the time in general. Like, “okay, what do I have to do today? Well, I have to clean the kitchen, and return the DVDs to the library…” I find that saying it aloud helps me clarify my thoughts.
Talking about speaking out loud to yourself, I find that if I say something to myself out loud three times, I’m almost guaranteed to remember it (like Kyla’s example - “Take dvds back. Take dvds back. Take dvds back.”). Any ideas why this might work?
Wait – two people use first-person plural?
Whoever you are, please reveal yourselves, so that I might kneel when I post in your presence.
If you did, how would you answer the poll? “Are you looking at me?” isn’t really covered in the options.
Oops, I hit the last one by accident. I meant first person plural, but really it could be that, second person, or first, depending on the situation. Come to think of it, it never involves talking to a mirror. Just internal dialogue.
I was almost going to leave off third person plural as an option, because I’m certain no one does that, but you never know!
I ask about the mirror for a reason. Sometimes I think to myself or talk to myself, and I refer to myself in a way that’s not worth noting, or one that I can’t remember. Especially when thinking, there really is no thought that takes on a person form. Even if I’m thinking about myself, and I don’t think I can explain this, I’m just thinking about me in a sort of conceptual way, but there is no “I” or “you” or anyone else. They’re just thoughts kind of floating, and they’re about me, but not. That didn’t make any sense, did it?
There is internal dialogue at times, which can be first or second person, depending on which way the wind blows. Often I am speaking aloud when no one is around, as opposed to speaking to myself, and it’ll be in first person. “Where the hell are my keys?!”
I’ve noticed, though, that particularly in front of the mirror, it is almost always second person. “That new lip gloss looks good on you,” and the like.
Edit:
Ha! Error! Err-ror!
The only thing I’ve ever said while looking in the mirror, is to myself and not to my reflection and it’s usually along the lines of “UGH, I look like crap today”.
So I guess that counts as first person then?
I’m not sure where “What the H311 is that?” would fit in when talking to oneself in a mirror.
I find it weird to talk to myself or talk to others inside my head.
Usually, in my head, I visualize the scene as though I’m watching it as an observer.
You should have included the option “I don’t talk to myself in the mirror.” I don’t.
I do talk to myself sometimes (because I’m all crazy and stuff), but never in front of a mirror. When I do talk to myself, I speak exactly like I would if I were speaking to someone who was standing right next to me. Except there’s nobody there. But I’m still talking to myself, not an imaginary friend or something. I don’t know how to explain it better than that. 
I’m speaking to myself, but I’m wording it as if I’m having a conversation with someone else.
We never talk to ourselves.
I checked First Person Singular, but it’s a bit weirder than that. Instead of the normal accusative “me”, I for some reason use the Latin dative form “mihi”, which is completely nonsensical.