DC Comics Universe and DC Nation #0 Spoilers follows.
This Joker take involving the upcoming Batman and Catwoman wedding is part of three stories in DC Nation #0; the other two involve a kick off to Justice League No Justice (full spoilers here) plus a Superman: Man of Steel prelude where Lois Lane is gone and a new character emerges (full spoilers here).
The Joker breaks into a home.
The homeowner is nervous.
Turns out the Joker is waiting for an invitation to Batman’s upcoming wedding.
The mail arrives and the Joker reads a letter.
He shoots the homeowner; it is not a wedding invitation he read, but a letter from the school noting the homeowner’s daughter has a lateness to school issue.
You are cordially invited to the wedding of Batman and Catwoman!