I don't know why -rep

Support button. Admin staff is usually swamped so don't expect fast answer.

In top of site there are sections: giveaways and so on and there is Support button

Also you can ask SG support to check his multiple wins when you create your support ticket for checking that -rep !

And don't worry much about it, every cool kid has one :)

Where do we check REP status?

don't worry about that rep. any smart user that trade with you would check WHY a negative rep was added, and since yours make no sense it will be ignored.

I had one guy give me a -REP for thanking him on a GA. He thought I was a bot or something I guess. I contacted support and they took care of it (since I don't trade) Be patient, though, they're busy as hell -- think it took a month for mine.

Or - Like Mullins said - ignore it. Anyone worth their salt would read the reason anyway, and it's gibberish.