this is “Western/British” humour. The real joke is for those of us who live in these countries is that using an undercover police officer to track what is harmless discussions about legal events (even the discussion about drugs is on a different site) would be such a level of overreaction that it can be laughed about. I appreciate people come here from all over the world, and for some this kind of joke might not be so funny (my extended family are from Malaysia and its only very recently that this country has started to approach “western” levels of tolerance and freedom…).