The meaning of WaterChestnut Sisters is another term for third sisters. It is when you become a certain age; most normally 10 or before a teenager and you’reguardian tells you that you have a WaterChestnut Sister.
“Oh my godguys, I just found out I have a WaterChestnut Sisters!”
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.