Let's be honest, most of us have been here. You've been a nice person, done everything right, and some trolls still down-voted your reputation. Or maybe you made one stupid choice that shouldn't reflect you as a whole. Then maybe it spiraled as people just saw the negative rep and down-voted it more mindlessly...
Don't worry. There are some things you can do.

Are you actually being a good player? Take a moment, just think. Objectively, what have you done? If you're still sure, then proceed to step two. If not... proceed to step two anyway, but this first step is important, because you need to know how you've been doing for this problem to be solved.

Whether you're innocent or not, this is still important. Just be a better player. That's it. Unfortunately, there are still plenty of people who just don't care, so if the problem persists, go back to step one, then two again, then go to step three. I think.

Ignore your reputation. It's just a number anyway, and if you focus on just playing the game and having fun, maybe your rep will go up too.

Go wild! Want to teamkill? Do it! Want to scream loudly whenever you get shot? Do it! The world is your oyster, so start cracking.

Fall down into a descent of twelve-year old humor and various swear words. If you can't seem to get to get back above zero, just remember, there's no limit to your reputation, down or up! And if you struck a ceiling, there's no way to go but down.

What is Intruder and what is reality? Does it even matter? Be the most unpleasant you can. When people say you hit rock-bottom, start digging.

1. Swear offensively
2. Hurt teammates
3. Cheat
4. Listen to steps 4 5 and 6

1. Compliment people when it's deserved
2. Communicate with your team
3. Do the objective
4. not listen to steps 4 5 and 6

Jokes aside, I made a group just for this. Try the Intruder Rep Help group at
http://sp.zhabite.com/groups/intruderrephelp

Details inside, yada-yada, I know this advertisement thing sucks and believe me, I hate it too, but it's the only way for this group to ever fulfill it's purpose.