Ergh, Moose, no matter what anyone tells you, you're smarter than you give yourself credit, since you pointed all that out (although obviously not in a great mood). Although you sound a lot like me before I just gave up on other people. You have an extremely high level of self-awareness and you're analysing yourself and what you're worried other people may think too harshly. :/
Basically as hard as it is to abolish the negative thoughts you think other people think of you if you don't put on an act, it seems to be your main issue. For example you say you don't like how you look - neither do I until I realised I hated how I looked soley because of what I perceived other people to think, now I just don't care.
I also understand how frustrating it is for someone to tell you to not worry so much, as the mind will do what it wants regardless of what other people tell you, especially if you're judging yourself too harshly. So I'm sorry for giving that answer. In my case, I don't even remember when it was, but I suddenly stopped worrying about what people around me thought. You say you're not reliable/thoughtful - if this WERE the case you wouldn't hate yourself for those reasons because you wouldn't have any friends at all. But you do.
You say people shouldn't tell you secrets because you'll gossip/talk behind their back. Let me ask you: If you told someone a secret would you be paranoid they'd talk behind your back about it? Would you really, for example tell someone that your best friend just confided in you that their father ***** them several times when they were 5? Would you laugh, gossip and tell other people about that? I don't think you would, so you likely do have self control you just annoy yourself (by worrying) so much you bury your emotions. Of course you might say "No I wouldn't joke about that behind peoples backs because of what other people might think when I laugh about it, even to the person I'm gossiping to", but it's doubtful, honestly. And this is coming from someone who has to fake 90% of his emotions in order to seem normal - although I'd rather do that rather than laugh if I hear about someone dying on the news. *Shrugs*
People should just accept you for who you are, as should you. I know it sounds ridiculous and utterly impossible, but this is from what I can tell (I know a bit about the mind) what seems to be bothering you the most. If you were to stand up in a group of people (that you knew...somewhat) and say "I'M ****ING SEXY!", what would your fears be? The major one would be that someone would say that you're not, you're ugly, you're worthess, or something similar? And if I'm right, you fear this the most because you've basically boxed your mind into automatically thinking that other people will immediately think the worst of you unless you're quiet/reserved or change your attitude depending on who you're talking to. Really, a lot of people do that without even realising it; you do realise it, I wouldn't (again easier said than done) worry too much about it. So you'd act different around someone that'd be loud and obnoxious to another person that'd be quiet and laid back - it doesn't matter. Most people would. You'd also act different around someone you're majorly attracted to compared to someone you're not.
You can't spend most of your free time just hating on yourself. It goes without saying that this is the last thing that'll make you happy. But at the same time you're the only one that can change yourself. I'm not sure on how much you've actually beat yourself up over these small (this is not downplaying it, just the issues themselves) things, does it really matter if you act different depending on who you're speaking to? No, although depressed thoughts and anxiety is the main reason you'd be doing so. There is no instant fix, although speaking to a professional (this is not condescending, you have no idea how much junk I've told doctors) how you continuously over-think worst case scenarios in your head. There are methods and even medication to help with these issues, no matter how much of a social stigma is associated with them (which would likely be your main reason for shrugging such ideas off, or simply thinking they'd be a waste of time).
I dunno, I'm better at talking about this stuff rather than typing, though I think you'll get the gist of things, although change is rarely instantaneous. :/
I apologise if my post comes across as judgmental, as that's not what I intended - but rather I wanted to reach a similar wavelength because I think I've been where you are once before.
Or you could always try what Luke said, although you'd have to get people to play Melee instead of Brawl with you. :D
@ Techno, good news. Just contain....yourself better in future. ^_^