Twos is a special word. While it can be used in relation to cigarettes, it makes more sense to apply it to joints.
It makes sense as a noun -
Basically the person who rolls it starts it - the person who has called 'twos' then gets it afterwards.
There is no threes or fours. It just flows from there.
got any twos? (weed, dope etc)
I'm twosed (baked)
TWOS! - order someone to roll a joint.
Im twosing (smoking a joint)