In English, if someone explains a simple joke that should be obvious they get the nickname "Captain Obvious", as the Wiktionary and Wikipedia say. Is there an equivalent expression in Chinese? If so, what is it?
Actually there are no exact equivalent in Chinese. The accepted answer only explained it literally and didn't get the culture background across.
I think the closest one you can get is 装逼犯.
装逼 means show off your knowledge that everybody knows.
犯 means prisoner. (People hate 装逼 so much. Some even say that it should be considered as a crime. Hence they call the one who is showing off a 犯)
If you are looking for Chinese equivalent of "Thank you, captain obvious!", try "装逼遭雷劈" (If you 装逼, you will get struck by a lightning). Well, we don't show our gratitude to 装逼犯.
The meaning is close and the cultural background is similar. But you can not use it everywhere. The problem is that 逼 literally means woman's sex organ so any 逼-related words are considered as swear words.
The term " Captain Obvious" has no equivalent in Chinese, it is part of a sarcastic phrase : " Thank you, Captain Obvious!" not commonly be used by itself.
A Cantonese sarcastic phrase, " 鬼唔知阿媽係女人咩？" ( who doesn't know mother is woman?) express a similar meaning. We say it when someone said something painfully obvious.
in Mandarin, it would be " 誰不知娘親是女人？"