My favourite is when TfL announcements about Stratford being a no smoking
overrides announcements about which stations a peak hour train is stopping
at (the Shenfield service has a complex pattern of stops at . As the east
end of platform 5 has no monitor and many commuters arrive on the Central
Line, being able to know if the train stops at your station is rather more
important than a stock announcement.

Or warning people that "the platform surfaces became slippery - this
is due to adverse weather conditions" when it's raining. Or the
absolutely useless and very long "security" announcements (aka "we
have CCTV"). Or the advertisement of the buffet (do they even get paid
for that?). It's like they have a contest to create the longest most
useless text ever.