Be inconceivable

I’m so confused right now. A Chinese boy told me that saying “有机会一起拉屎” to a friend is a friendly way to express closeness. I posted about it online, but now I’m feeling a little embarrassed! I looked up the direct translation, and it means “let's have a poop together.” Obviously, that’s not something friends say to each other in my culture. Can someone please explain what’s going on here? Is this really a common expression in China?[微笑R][微笑R]