Best: A BA FC meal served to We Who Were Upgraded after a 12 hour delay YVR-LHR; I don't know where they found roast beef that good in the middle of the night (Canadian time) but, wow.
Worst/serious was any number of servings of Western Airlines (RIP) "mystery meat" (I think that's where the term was coined.) Not only inedible but possibly hazardous.
Worst/humorous 1: An eternal turboprop leg overnight on Aeroflot between Leningrad (RIP) and Tashkent, where the midnight feast consisted of a piece of black bread with the consistency of a roof tile, a paper cupette of some jam-like substance, a hard (really hard) boiled egg, and a whole cucumber. All presented in your very own real PVC bag, which imparted its own perfume into everything. Comrades, the five year cucumber plan has been achieved - enjoy!
Worst/humorous 2: Dinner on an Adak-Cold Bay-Anchorage segment on Reeve Aleutian Airways (RAA) (RIP): Cold Spam sandwich on raisin bread, because the Cold Bay kitchen had run out of baloney. Really.