Just today I was walking back home after meeting some friends in San Telmo for lunch around 3:30PM, and low and behold, right on Av. de Mayo, between Chacabuco & Piedras, I saw two Asian ladies in their 30s, obviously tourists, with 2 suspicious people standing very close to them, talking. The scene looked suspicious, so I stood close by. The two idiots standing close to them, were "helping" them wipe a sticky green substance off of their backpacks, camera cases and jackets. They were telling them that something must have splattered them, when of course I know this scheme all too well. The Asian ladies didn't understand what was being said to them in Spanish by the 2 idiots but I immediately spoke to them in English and told them what was going on and they knew, and got scared and thought I might be part of it too. So they said "yes, we know, go away". So I stood a few meters away and waited to see what was going to happen, I stayed close enough for the idiots to see I was on to them, they scurried away around the corner and started cursing at me and giving me the finger. I stayed behind them pretending to take their picture with my cell phone and they ran like rats. As soon as they got about half a block away but still in my view I picked up a large empty beer bottle and threw it in their direction yelling "ladrones, ladrones, hay que lincharlos" they ran even faster and disappeared. This is what I mean, be VERY careful on Av. de Mayo!!