By the way another reason to believe that's really "stupido" and not "sapito" (or similar) is that when the movie came out nobody knew the name of the character portrayed by Alfred Molina. Since, according to those who believe Harrison says "Adios, Sapito!", the name "Satipo" follow a spanish word, there's really a little chance that the first-time audience would have understood it was a first name. Besides, in the whole movie the secondary character names aren't named (sorry for the pun) at all... Nobody calls Toht or Dietrich by name, Barranca neither... That would fulfil the viewers' minds with useless informations: what matters in such a movie is the characterizations of the single roles, that made them so charming, without knowing the anagraphic details of the marginal "personnages". So I really find the use of the vocative pretty useless in the economy of the scene and in a "systematic" reading of the whole movie... find much more fitting the word "stupido", in the bitter taunting context of the moment.
Another argument that bring water to this thesis is the fact that there's no way for the Authors (I mean Spielberg and Producers) to keep such an evident mispelling error in the movie, since the scene is quite easy to reshoot and very simple to repeat for Harrison... they would have just cut it.
So I'm quite propense to think that the "Sapito" interpretation is a suggestion inducted in the fans that knew too much well the name of Molina's character and maybe convinced themselves in hearing it (mis)spoken by Harrison Ford.
Besides, if you listen carefully to the phrase you can hear quite clearly "Stupido". I've tried listen to it again and again: it's just "Stupido".
P.S.: the argument based on the spanish word "sapo" as diminished in "sapito" in a - presuntively - ironical way is really too thin. The irony and the spirit of the movie is clear and understandable to an audience of all age and the quickness of the rhytm does not allow such linguistical intellectual digressions... much more immediate and in the spirit of the humour of Kasdan would be - once again - "stupido". I frankly cannot believe that a screenwriter would use such a difficult pun in such a hit-and-run movie.