There was the same "Reputation" thing some time ago, but it was taken away for some reason. Sadly, all the previous reputations are now gone.
Anyways, if you click the number of your or someone elses reputation, it opens up a new window where you can give your own reputation point to a another forum user.
There are 3 different reputations: "positive", "neutral" and "negative".
Hit the "Rate user" button on the top right corner and give the reputation you feel is most close to your feeling about another forum user.
So, in a nutshell: the more positive reputation you have, the more "badass" you are!