À propos humour under state socialism, and further to my irreverent Chinese lesson, I dare say this joke is in Hammer and Tickle, but I found it in Anne Applebaum’s (also excellent) discussion of various types of subversive manoeuvres in Eastern Europe (Iron curtain, pp.446–51).

I’m going to adapt it for China:

Two friends are walking down the street. One asks the other, “What do you think of Li Peng?” “I can’t tell you here,” he replies. “Follow me”.
They disappear down a narrow hutong. “Now tell me what you think of Li Peng,” says the friend. “No, not here,” says the other, leading him into the hallway of an apartment block.
“OK, here then.” “No, not here. It’s not safe.” They walk down the stairs into the deserted basement.
“OK, now you can tell me what you think of Li Peng.”

“Well,” he says, looking around nervously, “actually I rather like him.”

And here are some jokes from Hungary.