Groom's Speech
My cousin Craig was the groom and was about to make his speech at the reception.  This traditionally starts with the words "On behalf of my wife and I..." and everyone cheers.  But Craig (who was a little tipsy) forgot the traditional opening and just launched into the speech.
 
His wife Diane began tugging at his jacket, hissing "Say "my wife and I!"".  Craig ignored her and continued with the speech, batting at her hand like he was shooing a fly.  Diane continued with the hissing and tugging until Craig turned to her in obvious exasperation and said "Shut up, woman!"
 
There was a hideous, eternal second of horrified silence before Diane burst out laughing.
 
After 15 years of happy marriage and 4 kids, she still thinks it's hilarious and Craig still hasn't lived it down.