It's frowned on to invite yourself to a social engagement.
Shane and Tim are talking at the office and Tim tells Shane that this weekend he's going camping with some friends.
Shane wants to say something about Tim's camping trip.
Shane tells Tim that the trip sounds like a lot of fun, and he hopes Tim has a good time.
"Shane tells Tim ""that's great! I'll be there, too, when are we leaving exactly?""."
Tim is delighted that Shane has wished him a good trip and tells Shane he'll tell him all about it when he gets back.
Tim is annoyed that Shane just assumed he could come and is now feeling awkward as he has to deny him that possibility.