Hooo, here I thought this is a meme somewhat came from Oreimo's 人生相談.
C'mere, let's talk about the meaning of life...
Literal meaning. Originated from a sex scandal of Xu Chun Mei's. Caught by her husband sharing a bed with another young man, her excuse was, "We were just chatting while sharing the same blanket, that's all. We've never had sex." From then on, 盖棉被纯聊天 became a meme, an example of a blatant lie before having one's way with the other person.
Incidentally, when 我们来聊/谈人生 is interpreted alone, the phrase holds a different meaning: one wants to teach the other person a lesson, physically.
