Hee! It's funny, but the strength of the alternates you listed is pretty much exactly opposite here in the States. "Idiot" is usually kind of tame, unless delivered with real vitriol, but "bastard" is usually used for people really disliked, and indicates heartlessness. It's a titch old-fashioned, though. "Asshole/asswipe" and "douchbag/douche" seem to be the top of the line these days, though I have a strong preference for "dick/dickhead". "Tosser" isn't used at all. In fact, I suppose "jerk-off/jerk" is the only masturbation-related insult in common usage here.

Still, it's very amusing to me that the scale is swapped between continents.