Actor Allusion: Basil's goose-stepping in "The Germans" is deliberately reminiscent of Cleese's "Ministry of Silly Walks" sketch from Monty Python. Just check out the applause it gets.
Creator Couple: Cleese and Booth were married when they made the first season. They divorced by the time of the second one, but still could work together. This has led to rumors that the show ended because of their divorce, by people who didn't do the research about the timing.
Fake American: The actor (Bruce Boa) who played the American Mr. Hamilton was actually Canadian.
Fake Brit: Yes and no. Connie Booth had lived in Britain for so long that she could be said to be actually British. Also played with in "Gourmet Night," where she sings in a perfect but annoying American accent.
Fake Nationality: Manuel, who's from Barcelona, is played by Andrew Sachs, a German-born British actor.
Grandpa Joe is on the verge of having a large garden gnome inserted in him.
Mrs. Hudson is one of the guests at Basil and Sybil's anniversary party.
Old Shame: No one was really happy with how "The Builders" turned out. Cleese notes on the DVD that it was the only episode not filmed with an audience, and he felt very awkward through the whole thing with no reaction to play off of.
Real-Life Relative: John Cleese (Basil) and Connie Booth (Polly) were married when they wrote and acted the first series (1975). By the time of the second, in 1979, they were divorced, although they were on good enough terms to keep working together.
Word of God: John Cleese said that they had little intention of creating catch phrases (Manuel says "¿Qué?" a lot, for instance, because... well, how could that not be the case?), though they did eventually realize that the "He's from Barcelona" line almost got funnier each time they put it in. Especially when Sybil and Polly are eventually forced to use it.