Rule 8: If this is your first night at fight club, you have to fight.
http://en.wikipedia.org/wiki/Fight_Club#Plot_summary
Basic rules that come to mind to keep it hacker centric could be:
1. If this is your first night to Hack and Tell, you must
Tell.
2. Before leaving Hack And Tell you must vote yay or nay
on each Tell. If your Tell has less than X votes, you
are not allowed back for Y weeks.
3. If you're just returning from a Y week layoff, you must
Tell.
4. You must have a Tell every Z weeks.
I'm not at all certain what the correct values for X, Y, and Z are. Z would obviously depend on the group size and time allotment. I think voting should be anonymous and not announced until after everyone's left so voters are more likely to be honest.If it gets popular I could even see having a Hack and Tell website that hosted videos of "successful" Tells and so forth. Going out on a limb and having national votes to try and get a group of hackers together for a nationally voted "Best Hack" event or some such.
Could be fun.
[ed: formatting]