The word was invented by my buddy in 1989. He was
making mac and cheese, but had no butter. He spit
in the mix, instead. Me and another guy were watching, and he looked up guiltily. He said, "I can't believe I did that. It's so sleazy. It's so assinine. It's... slass." We all busted up laughing. Therefore
the definition means "part sleazy, part assinine; both sleazy and assinine." The word has since grown to mean something more along the line of "generally negative."