A term that referred to a person who listened to Heavy Metal music, wore long hair, perhaps a leather or denim jacket with metallica or iron maiden patches, etc..
Was used in high school among teens and young adults in the 80's to early to mid 90's when metal music was fairly popular in some circles.
The Dumbest person on the face of the earth. A Hammer gets in people's ways and annoys them while they are trying to work, and, while he is supposed to be working, stands around and acts stupid. If you have someone at your workplace who follows you for the sake of following you, has his hands in his pockets, drills holes in the wrong places, or drops your flashlight and breaks the bulb, and you are on a construction site, it is likely that you are working with a Hammer. If you are a Hammer, you may as well make a career out of stocking shelves at Walmart or being a dishwasher at Denny's.
Hammer, PLEASEgo be a moron elsewhere so that I can actually do my Job.