I get this one whenever we have a delay situation caused by the late arrival of the operating aircraft and a PA has been made to this effect.
Pax - Excuse me, is this flight boarding?
Me - No, we have a slight delay today, due to the late arrival of the operating aircraft, as soon as the aircraft is here, we will board you as soon as all incoming pax are off the aircraft and we have completed the cleaning and our safety checks.
Pax - You dont understand - I need to be on that flight.
Me - (turn and point towards EMPTY aircraft bay) - as you can see, there is no aircraft here yet, so we will have a delay in boarding - whilst we await the arrival of the aircraft
Pax - but is says on my boarding pass - we will be boarding at this time.
Me - as I have just explained to you blah blah blah (repeat myself for like the 5th time)
Pax - Are you listening to me - I need to be on that flight!!!!!!!!!!!
Me - Look, see down there - no plane - you cant get on it, if its not here, please take a seat and I will personally escort you to the aircraft once we have an aircraft to board.
Pax - you could have just told me that in the first place.
God love em!!!!!!!!!!