So I'm curious.. How long does someone's bad karma stay on them? If they were say -25 how long would it take for that to drop off?

Karma degrades by 1 point a day toward 0.

Oh so making a negative report for someone the next day that karma will be at 0 instead of -1?

Yes. At least in the game.

If you report someone here on the site, it never degrades. However, if you report me today for -1, then report me tomorrow for -1, it will only count as -1, instead of -2.

On the site, you can only ever give someone -1 or +1 that will count towards their overall karma score.

In game the karma degrades 1 point each day.