The terms "jerk" and "a--hole" have meant "mean person" to me as far back as I can remember. Those were the earliest playground definitions. But watching older movies (sometime in the 80s and earlier), I've noticed that they both used to mean "idiot." Steve Martin's The Jerk is an obvious example. I always thought that movie was about a guy who was, well, a jerk. A person who was unkind for selfish and douche-y reasons. It wasn't until I finally saw it that I realized it meant The Idiot.
Watching Spaceballs as a younger kid was similarly confusing. (I shouldn't have been watching it at that age in the first place, of course, but that's what friends' houses are for.) There's a whole bit when Dark Helmet discovers that a large portion of his crew is made up of cross-eyed morons, all of whom possess the surname "A--hole." I didn't get why these dumb guys were called that. They weren't mean, they were stupid!
I don't know when the transition from "idiot" to "mean person" took place, but I don't know anyone that still uses those terms in the earlier sense anymore, so it seems to have been a universal shift. Anyone else notice this? When did the change occur?