By posts.
For example, I wrote something about one of your hobbies and you liked my post, so you give one (1) reputation point to me by applying it on postbit, directly on the post that is subject to your liking.
For this system to work, there will be a need of some adjustments. For example, positive warnings (in this case reputation) must NOT result with a ban.

Is it possible to ban members with negative reps? (e.g. -20 reps can be enough for ban.)
The other point, not only moderators or admins, but all members shoul give reputation to others. I think this can be done in templates. (changing the code of usergroups, right?)
With some changes, can we write why we give points to user?