Checkmate in 4

  I don't know if "chessaholics" would call this the "oldest trick in the book" or not, but after my friend beat me with it I felt like I got skunked!  Alas, I discovered there are some out there who are not aware of this.  I do let people know not to feel too bad and that it happened to me, too.  I don't try this every single game either.  Is this unsporting?  Please let me know as I am still relatively new to chess and would like some more information on "decorum".

Thanks!