Irish captain once announced an apology for the delay in taking off.....
"...and as soon as the private jet and little fokker in front of us have left, we'll be on our way".
Went down like a fart in a spacesuit to some of the harder hearing pax!
My only advice is to judge your audience on boarding before atempting humour. Naturally a Majorca flight is very different to a Munich flight. Do not add humour to safety PAs as you'll end yourself in trouble.
The best PA to add humour is on the landing, especially if you'd had a bumpy one or a turbulent flight.