Reinforced Autoclaved Aerated Concrete: a type of lightweight concrete used for constructing rooftops after tin and asbestos roofs where banned. It has a lifetime of 30 years so it causes a lot of financial problems because it has to replaced in halls and offices.
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.