Well, I'm American, and there were definitely bits in that book that totally failed to translate for me. For instance, "Ford Prefect" seemed like a perfectly normal name - IMO the American edition should've changed it to "Ford Escort".
But being self-deprecating was not one of them. I feel like I'm surrounded by Zaphods, or something, and I'm not sure when it happened.
I’m reminded of Arthur Dent (British) in the Hitchhiker’s Guide telling Zaphod, modestly, “oh, it was nothing” about something great he did, and Zaphod responding along the lines of “oh, it was nothing? In that case forget it then”, which was not at all what Arthur intended.