I personally occasionally use deadass. I just can appreciate the feeling behind it. I also vaguely remember using it in the 90s but maybe that's my personal Mandela effect.
Discussion
It wasnt any particular slang, it was the whole package.
Im not exaggerating, he had one Monster energy drink in each pocket.
https://www.dictionary.com/culture/slang/deadass
It isn't my own personal Mandela! Sorry, I had to find out.