I remember a tale of a CC member who sold a pax 200 cigarettes on the duty free service & the pax complained in a rather loud notice me voice that "you've sold me 200 cigarettes & now you're telling me I can't smoke on the plane?"
to which a rather swift "they sell condoms in boots madam, need I say more?" answer was given by said CC
Also I work on the railway & although its not flight related it still shows that pax regardless of the form of transport don't think before opening their mouths...
I once opened the train doors at a station to be asked "does this train go past our Sheilas?"