Have to say I like gobsmacked, and adopted it, laughing, when I first heard it, maybe, hmm, 15 or 20 years ago. I was eating with friends when I first used it and my hostess looked at me and said, "What was that word?" and I used it again, illustrating it by bugging my eyes out in astonishment and smacking my hand over my mouth.
I also love the Irish gobshite, a perfect description of someone who is kind of lazily stupid, equivalent, perhaps, to liúdramán (pronounced, roughly, lyoodhramawn, with the emphasis on the first syllable).