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 -
Adjective -
imperative -
verb
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.

when someone smokes a fag, you say twos to get half

An exclamation made to show ownership of a seat in a room. When getting up from one's seat, proclaiming twos leaves this particular spot branded by the one who was sitting in it until they return. Sitting in someone's seat after having called twos often times leads to both physical and verbal attacks. Twos must be called while still touching the seat and is invalid if called while standing up. In the instance that he who called twos is to take a seat anywhere else, twos is immediately cancelled and the seat is once again up for grabs. Twos is not valid if he who calls it leaves in a vehicle with expectations of getting their seat back when they return. One is allowed to take a bathroom break and call twos without the toilet counting as another seat.

How long a commercial break lasts; i.e., two minutes and two seconds.

Obviously

2+2=4

When you drink from 2PM until 2AM then promptly pass out.

Play on words based on the phrase Catch 22; see you on the other side.

-The ultimate numerical paradox.

-A perfect balance of one on each side for perfect harmony, never being able to counter balance since its perfectly even. Yin and Yang. You have a brain for logic, but then you have the heart to counter balance with emotions.

-Not only used for balancing, but combined for the ultimate pair. In order to start a family, you need 2. Every hero needs a sidekick. you have not 1 but 2 eyes for ultimate depth perception. 2 arms, 2 legs, 2 ears, 2 lungs, 2 testicals.

-most powerful number in math. 2 is the number most divisible into other numbers (not counting 1 since one is itself and more or less is the building block of all numbers). 2 is what we build off of. It's so simple, yet so strong. Subconsciously you know this to be true since when refering to something simple or basic, we say "put 2 and 2 together." Why dont we say "put 1 and 1 together?" We don't see 1 as a credible number, holding 2 in higher regards.

-2 is the only number that can't make a shape(number of sides). 1 is a circle. 3 is a triangle. But what is 2? Think about it...

-There are only 2 things to do with your life, live or die.

-For every action, there is a re-action. one things leads to one other thing. that equals 2. we live our lives between 2's. we go to work to get money to live. we work out to get buff. we eat to satiate our hunger.

-Everything has an opposite, or equal other, that makes them a pair of 2. There is only good or evil. There is only right or wrong.

2 packs quite a punch, don't you think?

The number that (usually) comes before three. Square root of four. Also the amount of people it takes to tango.