If something is "dope" it's like saying something is cool or awesome. For example, "that party last night was dope, man."

And if something is cooler than cool or beyond badassery, then you can say "the dopest dope." For example, "Did you see Neely Von's lastest travel pics? They are the dopest dope, grrl."

Historical perspective: This term used to refer to drugs, specifically heroin (not marijuana). Like many online jargon terms, it has morphed to mean cool, and can also mean boss, hip, terrible, outta sight, monsta, gangsta, and dynamite.
See also : millennials  thirsty  salty  swerve  done  
NetLingo Classification: Online Jargon