My worst one was a refuelling announcement on a turn around...
I got through the first bit ok, (seatbelts unfastened, remain seated with the aisles clear etc)...
Just before the end of the PA, I was distracted by the Captain - and in complete 'auto mode' after the brief distraction (about 20 seconds), I returned to the last line of the PA:
'Please dont strike matches - Thank you!'
Needless to say the pax (who were regulars and knew me) had a bit of a laugh.
Then theres:
Welcome to XXX, the local time here is September 1954.