Inbox(1) is the sending of a message (often by electronic means such as by facebook or email) with no point other than to provoke the receiver. The message contains nonsense and is designed to make the receiver think that they may have a meaningful message (when they see the status of their inbox: "inbox(1)") when in fact they have no messages.
"lol...I inbox(1)ed you!"
J: I have a message :)
J: Oh damn...you inbox(1)ed me -again- ;(
M: Mwhahahaha :D