Depending on the person that you are doing it for, these may or may not be approprate things for the comment on the cake. If these offend anyone, I apologize in advance.
*Marriage is a three ring circus. An engagement ring, a wedding ring, and suffer-ring
*If Love is Blind and Marriage is an Institution, then Marriage is an Institution for the Blind
*Marriage,five minutes to get in and a lifetime to get out of
*My husband and I divorced over religious differences. He thought he was God and I didn't".
*A woman has the last word in any argument. Anything a man says after that is the beginning of a new argument.
These were gotten off of http://www.divorcehq.com/humor.html