housei my friend

A joke in Downtown no Gaki no Tsukai ya Arahende!!'s 2013 New Year's Eve Special: Zettai ni Waratte wa Ikenai Chikyuu Boueigun 24ji (2013).

Here's a good English explanation: Danbooru comment #1225449.

Here's another one:

Reference to the 2013 instance of the annually recurring "Absolutely No Laughing" segment on the long-running TV show Gaki no Tsukai, which was called "Absolutely No Laughing: Earth Defense Force". Part of the skit involved an alien being discovered in a cupboard, which suddenly decided to declare its eternal friendship with Tsukitei Housei by saying "HOUSEI MY FRIEND" (in English). Eventually this caused Housei to be branded as a traitor to Earth, when the alien invaded an Earth Defense Force base, was captured, and indicated that Housei was its friend. Full story on ニコニコ大百科, abbreviated video clip of the segment on YouTube.