Is that a British thing? I don't think I've ever heard that before.
Sorry, I didn't realise I was being overly local! But yes Boblawblah is quite right. I think the Dictionary,com definition is pretty spot on, which gives the meaning of pseud as "a person of fatuously earnest intellectual, artistic, or social pretensions".
"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"