Well what does the 'thankyou' at the end of a PA mean? Thank you for listening to me giving you the information you want? (you don't actually have a choice- you're under the speaker!). The pilot is doing all the work getting this information assembled and imparted- the pax should thank him for going to the effort. What the 'thankyou' at the end of most PAs means is 'I don't really know any way to exit, so I shall just mumble thankyou and cut off.'
Slag, you are up 5 pounds. The PA standards amongst the other airlines I fly with are atrocious. BA went to a lot of trouble giving us courses on what people want to hear, and I slipped a lot of them in there for free. I do hear the most awful PAs outside of BA. In BA, there is a gigantic problem with desperately overblown Cabin Crew PAs, to the extent most pilots minimise what they say out of sympathy for the passengers undergoing non-stop PAs about everything under the sun from the Cabin Crew (then in German and French and Italian and Spanish), and finally when all you want to do is get the hell out of there, they touch you for charity with another PA.