First known usage was by the 1980's rap song "Just a Friend" by Biz Markie. Its a "rated G" way of saying "oh shit"
So I came to her room and opened the door
Oh, snap! guess what I saw?
A fella tongue-kissin’ my girl in the mouth,
I was so in shock my heart went down south
So please listen to the message that I say
Don’t ever talk to a girl who says she just has a friend
A weapon consisting of heavy brass (the cheap plastic ebay ones dont count) that have holes for you to put your fingers through, in order to get a grip and form a fist. Once this is done, you can use the weight and hardness of the brass to injure soft flesh. Pretty effective at ruining people's day, but if you dont know how to fight you may get it taken off your own hands and then used against you. Imagine that.
You try to get slick, you bust a little chuckle, you're gonna get smacked with my gold finger kuckles.