I’ll start:

BA8 Tokyo Haneda to LHR. A 14 hour daytime flight leaving at 09.35.

Lights off and windows blacked out for 10+ hours (although there’s nothing to see as it’s dark over the Pacific and Canada for most of the flight).

Lunch at 11am then no service whatsoever in J for the next 10 hours until the light meal 2 hours before landing. If you wanted a drink you had to go to the gallery.

I can’t think of a more miserable flight I have taken but I’m sure there is worse. Suggestions here for the worst BA flight / route.