Prisoner's Dilemma is an incredibly interesting game because it forces a paradox on you: the most rational thing for an individual to do is always to defect/be a jerk (because in all possible states of the word, defecting gives you the highest reward), but by being "rational" you are damning you and your partner to a sub-optimal outcome.
I don't see how the same paradox applies here.
Maybe I'm a curmudgeon, but I don't think that comparisons to the Prisoner's Dilemma should be handed out lightly.
I guess you're always better off writing tremendously offensive things ("defecting"), because you'll either get $20 or you "get" to post the thing on your friend's wall (which, since we're 12, counts as a victory, naturally). But the game will instantly hit equilibrium: we all post offensive things, we all put money in, and nothing ever happens.