I love this TED Talk by Jane McGonigal on Massively multi-player thumb-wrestling:
It is a great conference or classroom hack, to break the pace of a lecture while creating an awesome atmosphere. As Jane mentions in her talk, oxytocin, the “bonding hormone” which plays its part in intimacy, is secreted by the brain after holding hands for just six seconds. So this game makes people happy.
The Austrian artist collective monochrom came up with the rules of MMTR, which as available online.
In addition to the classic formation, one could use their other hand to form nodes of a human network of thumb-wrestlers.