From here:

Some History about Playing the Dozens

"Snaps" carry references to one's relatives, especially one's mother. The expression "Playing The Dozens" means to taunt another person by taunting, kidding, "jiving," teasing or insulting their family--in essence, to use "snaps." This "gaming" has deep roots in the humor, personality, and social relationships of Black Americans.

Across the coutry there are many names for Playing the Dozens, such as capping, cracking, bagging, dissing, hiking, joning, ranking, ribbing, serving, signifying, slipping, sounding, and snapping. While the names vary, the rules of the game remain the same.

Playing the Dozens is more than a game of fun--it is a battle for respect. It is an exhibition of emotional strength and verbal agility, a confrontation of wits instead of fists. The dozens is a war of words--perhaps the best type of war there is.

This verbal tradition combines elements of boxing, chess, and poetry. In a contest demanding the poise and power of a boxer, the aim is not just to win but to deliver a knockout. Fought before a crowd, the verbal pugilist wants not only his opponent but all who witness to think twice about confronting him or her again.

Like chess, playing the dozens requires a strategy. To win a battle, you must stay two or three snaps ahead of your opponent. Even as you are being attacked, you should be setting up your counter-snaps. Should I say something about his Fayva shoes? Or perhaps attack his fat sister? I'll save my best shot for his K-Mart cologne. This is the type of strategic thinking that makes a master snapper.

Painting humorous pictures of your opponent through words is key to becoming a dozens laureate. "You're so fat, your blood type is Ragu" is an actual snap fired in a legendary battle at New York's Frederick Douglass Projects. The picture created by this verbal H-bomb still haunts the victim to this day.

Snaps have to be delivered properly in order to work effectively. The setup--"Your mother is so fat..."--is a classic example of how to cock the hammer for the ensuing snap--"...she broke her arm and gravy poured out." Like the firing of an individual snap, the delivery of a series of snaps requires a rhythm. You might loft your initial snaps slowly, then fire the successive barrage with increasing speed.

Members of the audience serve a number of fundamental roles in playing the dozens. First, they are needed to witness the event. Playing the dozens without an audience is like launching fireworks in daylight. Second, they are responsible for recording the verbal history of the battle, and then for spreading it throughout the community. Third, they fuel the conflict by responding to the snaps, and it is their reaction that determines the ultimate winner.

Some Tips for Playing the Dozens

How do you get the audience on your side?

Drawing the crowd's laughter at your opponent is what wins battles. To elicit laughter, you must recognize what makes the audience laugh. First, your snaps must be clever, original, and appear to have been crafted solely for your opponent. Second, a snap that touches a shared reality is a good bet. For example: "Your family is so poor, your father's face is on food stamps." Third, after snapping, you should occasionally eye the crowd. This will keep them laughing at your snaps, in fear of becoming a target if they don't.

Why is "your mother" so often the subject of snaps?

Like the proverbial "Mom" tattooed on a sailor's arm, there is nothing more dear to a man than his mother. Mother snaps go to the soft underbelly of your opponent. In the early days of snapping, mother jokes were the big guns. Their deployment was saved as a last resort--one that often elicited the response, "Don't talk about my mother!" Nowadays, "your mother" is a stylized opening of most snaps. In fact, they are also commonly referred to as mother jokes.

Where is the dozens played?

In playgrounds, on subways, at pizza parlors, in the classroom, on street corners, in locker rooms...anywhere peers hang out. A game of the dozens can be sparked by contact on the court or words exchanged on the street. Increasingly, you can see the dozens played in comedy clubs as comedians defend themselves against audience hecklers. Some comedians get more laughs from snapping on the audience than from their routines.

What is the distance that I should maintain between myself and my opponent?

You may get as close as you want to your opponent without making physical contact. Spatial relations are an important aspect of the game. You can use distance to heighten the effect of a snap. A snap punctuated by a hip shake, fluttering eyes, or lewd hand motion needs space in order for the audience to appreciate the effect of your body language. When the snap is composed of words alone, closing in on your opponent may enhance the power of the attack.

Do women play the dozens?

Historically, the dozens has been a male experience, but women are playing in increasing numbers. Fortunately for men, most battles remain within the sexes.

What do you wear when playing the dozens?

It is smart to wear clothes that do not give ammunition to your opponent. Battling while wearing a strange outfit could be a death wish. If you sense that you might be drawn into the dozens on any given day, be prepared not only with your wit but with your wardrobe.

Do you need a loud voice to win a game?

No. What is important is that you be aware of what kind of voice you have, and use it to your advantage. If you are soft-spoken, do not try to yell, the audience will misinterpret the straining of your voice as a sign that your opponent is landing his snaps effectively. Instead, speak softly and carry a big snap.

In short, the dozens is a thinking person's game. However, the tradition lives on because the game has soul. Ultimately, mastery of the dozens demands that you go to that place where humor, anger, joy, and pain all reside. It is from that cauldron that the greatest snaps are born and delivered.

Here's a link to some common snaps.

Peace.