A popular misconception by the 21st century kids that "rad" is short for "radical", whilst it can be, it is more popular with ex-hippies from the original counterculture of the sixties to stand for "rock and drugs", ergo, rad. Though, it can still be used in context as, "that party was really rad," but therefore implying that there was rock and drugs at the party.
L: What ever happen to justplain sex, drugs, n rock n roll?
B: I don't really know why they left the 's' out, I guess you could say rads.
Abbreviation for Really Awesome Dudes. Used in the context "Hey man, you're rad," it is also an organzation of strapping men from Pine Plains, NY. Who are Really Awesome. Dude.
Hey bro, you're so RAD. You are a really awesome dude.