Semi affectionate term used to describe a female who chooses a career path in one of the manual labor type trades historically & currently dominated by males. Like auto mechanics, welders, carpenters, truck drivers, Sheet metal fabrication, and the like. To identify a Nasty Gash (or in mixed company "NG") such women dress and act much like their male counterparts. This term does not in any way mean that the female is autiomatically a lesbian, or decidely unattractive in any way. Many "NG's" would actually clean up rather nicely if they ever bothered to, or owned any clothing that was even remotely feminine. It also carries no negative connotation as to their abilities in said trades. Additional verbage would be used to describe such.
"We got a new "Nasty Gash" starting at the shop. We'll have to see if she's any good or just a token hire"