Well the Reefer part is obvious, I think, and is not related to any herbs and spices. Been there, done that....suffered from so called "paranoia" syndrome.....gave it up.
The Johnny part may or may not be obvious. I've always liked to refer to some people as "Johnny whoever" on occaision. Like "Johnny Salesman" or "Johnny Truckdriver". Such as...."So Johnny Truckdriver passes me and then gets into the slow lane again and slows to 70kmh!".
I must point out, too, that this characteristic of mine was adopted long before the arrogant "Johnny Fairplay" got his 15 minutes.
While I'm at it, the avatar has somewhat of a double entendre. I found it doing a "Salty Dog" image google search. It is that of a sailor, as most people refer to them (aka seaman; deckhand). It is representative of my maritime occupation and since reefkeeping is also marine related...well...there is the double entendre. Johnny is a sailor that is also into reefkeeping.
Cheers
,