I am c/c and god does this annoy me!!!
I will do extra PA's as we pull on to stand and sometimes this does not work. In fact on several occasions if someone has stood up I will do the following ....
"once again ladies and gentlemen PLEASE remain seated until the fasten seatbelt sign is switched off, and yes this does include the passenger wearing the black jumper!"
Not entirely professional i know but it makes people laugh and a certain passenger look very embarassed.
The best one I have experienced recently though is when we get the PA from flight deck...
"cabin crew doors to manual"
Its amazing how many pax believe they are suddenly crew and can stand up with us.