Although I'm normally pretty good at understanding English-language idioms and jokes, there's a recurring joke (?) I don't get, which Google didn't help with either.
There is a character who is a Soviet kosmonaut, and his name is Pieter Jakov (isn't that rather an unusual transliteration of the first name?). Apparently, the full name is so hilariously funny to the American characters that they have to carefully restrain their facial features when saying or hearing it. The kosmonaut himself doesn't seem to be aware of this, even though he is supposedly completely fluent in English, without even having a British accent - the latter being portrayed as a special accomplishment.
I was all ready to post this, when I said it out loud again and realised that this might possibly have something to do with the fact that the last name might, depending on how you pronounce it, sound like a colloquial term for masturbation. Is that it, or is there something else involved? It seems rather infantile, to be honest, if that's the whole thing. It's not as if there weren't plenty real-life people whose first names are euphemisms for, say, the male genital