There was a playwriter and a critic and basically they just hate each other - they were french.
So when the author launched his new play, he sent two tickets to the fellow critic with a note "come with a friend if you ever happen to have one"
The critic sent back the invitation for the premiere with a note "unfortunately I wont be able to make it for the first show, but I'll go to the second show, if it ever happen to be one"