A person who likes to take drugs, mainly heroin. They look all fucked upp.
Me: WTF! Get out of my backyard! Fucking Yonkie!
Yonkie: I am not a yonkie! *Sniff* I just like the feeling of empty syringe.
Me: Yeah right! And what's that? I'm gonna tell you, that's HEROIN, FUCKING YONKIE!