You accused someone who's not only liked on the forums, but is staff and had full right to do what they did. That's why you lost rep.
Did you look at the User CP list with your points and who gave them to you? Usually people give you reasons why.
And they don't lose rep, usually. They might, yes. But that thread is to take care of members and threads by banning or deleting when it's judged to be due.
Do you understand now?