I have heard 2 PAs that stood out for me.
First was arriving back to LHR from the US where the Captain very sincerely announced that "..the cabin crew would like me to tell everybody on board that you may have all boarded as passengers but you will all disembark as friends...." - I had to reach for my sick bag.
Second one was very funny, the CSD on a BA flight, where one of the movies you could watch starred Kurt Russel, mentioned Kurt Russel in every single announcement he made. Very amusing.