I once used the word twat around my then-girlfriend and she "corrected" me, insisting it was pronounced "twah". Turns out she thought people saying it were trying to use the French word toit and mispronouncing it. No idea why she thought anybody would want to call somebody else a French roof.
You're friend wasn't the first to make such a mistake. There's a poem from 1841 by Robert Browning, called Pippa Passes, in which he misunderstands the meaning of the word "twat." Apparently he thought it was the name for part of a nun's outfit.
But at night, brother howlet, over the woods, Toll the world to thy chantry; Sing to the bats' sleek sisterhoods Full complines with gallantry: Then, owls and bats, Cowls and twats, Monks and nuns, in a cloister's moods, Adjourn to the oak-stump pantry!
That reminds me of the time I went to a roller disco as a child, having just seen Mr Bean at the pictures that afternoon (this one: https://en.wikipedia.org/wiki/Bean_(film)). There's a bit at the end where Mr Bean's in a convertible waving at everyone he sees, when this hard knock rides up on a motorbike and responds with the middle finger, so Mr Bean naïvely copies the gesture and ends up sitting high up on the back of the seat giving the finger to everyone and no one. Ironically enough, I was too young to know what the finger was, so I just naïvely copied the gesture myself and started skating in circles around this sports hall giving the finger to everyone and no one. I don't remember anyone doing anything about it either!