"wrote on 14 Apr 2005: Read novels and comic books. ... gutter of American speech and it will cleanse your soul."
"And your mind, of anything resembling a language governed by simply understood rules. And get right down in the same gutter, and it will dirty your mind and your soul. If garbage is what you want."
The point is that language as such isn't governed by simply understood rules. All grammar for living languages is only an approximation of the language as it is used by native speakers - even by the so-called educated native speakers of the standard form of the language.
The connection between language and logic is tentative, to say the least.
Words move from slang and jargon into the main stream of the English language all the time. It's actually one of the joys of the language, even if some of the terms may not appeal to some of us.
And the OP did specifically ask to about where to find American English slang.
Regards, Einde O'Callaghan