A Sambrook is a person that asks too many questions about a particular event. You ask them on a nightout and they immidatley want to know who's coming, what time, where, what should they wear, what's the occasion. By doing this they take all the fun out of the event before its even started!
Harry wanna come to a BBQ at mine on Sat? "what time does it finish,who's going, what we having, do i need to do anything? For Christ sake Harry don't do a fucking Sambrook, you coming or not?
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.