I'm back and with more:

Lightsabering- When the joint's burning but the paper isn't so it looks like it's glowing.
Reefer- A pure weed joint.
Hot rocks- The little rocks that fall off a joint of solid.
Packed- When a joint's got more weed in then usual.
Bumming the joint- Getting the paper round the roach wet.
King L- A joint rolled out of 2 king skins stuck like this: |___
Rolling an L- When you run out of king skins and use the small papers in an L shape.
M tray- A peice of card folded like |\/| to set a joint up on.

I'm sure there's more but my mind's gone blank again...