Witty, but my head would almost crash into my hands when I heard this if I didn't think the speaker was really really smart so that I could trust that the exercise would be instructive in a particular, useful way. If I don't trust the speaker that much, they need to start giving me specific concrete things related to self-development or I'll not be very confident in their ability to help me.
It's too late by now to help the OP, but a few points need mentioning:
I recommend paranoid debating / the Aumann game / calibration exercises with trivia (answer trivia questions with confidence intervals).
Wits and Wagers has lots of good quantitative questions for calibration exercises.
The same equipment lets you play the updating game (divide into small groups, come up with point estimates individually, then update on others' numbers and see whether on average it moved you closer),
Werewolf? Making correct assessments of other's behaviour and avoiding group think are useful rational lessons. Its also fun!
I'll cut to the chase:
Running a Less Wrong-like self development group tonight and have failed to prepare anything insofar. starts in 2 hours.
Any games that I could pull out that will interaction and critical thinking?