I have only ever once seen a passenger sworn at by a member of staff
without provocation. Said incident occured on a 430 bus when Pax
touched oystercard on reader and got a green light (70p deducted).
Driver called Pax back and asked him to touch his card on the reader
again... red light (not supprisingly you can only board the bus once).
Driver asked passenger to get off. Passenger said "No, It has already
taken my 70p off". Driver said "**** off". Pax remained on the bus
and driver drove off.

On a later journey I saw the letter of response from TFL which said
meerly "Your complaint has been passed to the relevant bus company"