A japanese word that roughly translates to "black person" with "koku" being the color black (or dark) and "jin" meaning man (although gender is typically neutral). The word kokujin is not derogatory unlike the word kurombo and should also not be confused with gaikokujin (non-japanese person).
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.