In downtown baltimore, a missile is most commonly an awesome bag of raw heroin. If it's of a good quality and there's a good amount, then it's a missile. This term is also used to refer to other drugs, but mainly heroin. In the last year or so it has seen repeated use as a replacement for "the bomb". In this context it can be used to describe anything of an exceedingly high quality.
I once was buying a bag of weed and had it broken down for me by a native. I commented the bag was a bit small, and he replied to me, and I quote:
"don't even worry about the size, baby, it's a <i>missile</i>"
I asked him what that meant and he told me it was like the bomb, except it gets shot straight into your nose/lungs/veins.
A nuclear missile is better than a regular missile.
That dope I got from Jimmy The Hat was a fucking missile, I shot up yesterday and I'm still fucking wasted!