Murray--

The first time I remember hearing the word 'cowboy' used in a US context in the manner you describe was in the 1972 Charles Bronson movie, "The Mechanic." Bronson is a hitman, and in referring to some competition in a disparaging manner, he calls them cowboys.

I'm thinking cowboys used to get a hoot out of riding into town, shooting up the saloon and riding out again--a lot of sound and fury signifying not too much. (Sort of like your average Mudcat thread.)

Whoa! I was about to tell you about the "second time," but now I realize this had to be earlier, because I was "in-country" in 1969-71, so I couldn't have seen "The Mechanic" till after. Anyway, as I came & went through Saigon, I heard that there were nefarious characters who rode mopeds downtown. Dumb GI truckdriver comes to an intersection, puts his arm out to signal left turn; the moped guy bolts past and peels off his expansion-band wristwatch on the run. They were "cowboys."

Since then, I have heard repeats of the same idea, not a lot, and probably more in movies than real life, but it is an American usage too.

CC