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This is just a wild stab in the dark, But might it have been Red Dwarf?
Not blonde, but definitely running around in their pyjamas: The Hitchhiker's Guide to the Galaxy?
Hitchhikers Guide to the Galaxy, more or less certain. ""Space," it says, "is big. Really big. You just won't believe how vastly, hugely, mindbogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space. Listen..."
A live action show. All I saw was part of an episode. It was set in outer space and it had this blond dude who was possessed by aliens or something and was running around in his P Js. I'm a huge Trekkie so I think I would have recognised it if it was Star Trek. I think a guy was eating pizza at one point. And it began with a speech on how amazing space is with a picture of a spaceship.