1) Expats
2) Bars/ Boliches catering to expats
3) Friends of expats
4) Argentinos who are heavily influenced by American culture (TV/ Film)
Halloween isn't everywhere. You have to look for it. But if you are in certain parts of town and/or if you go to certain bars, you can find it.
-Nappy
PS- I've always been partial to the chicas who go as slutty nurses. I think that there is a certain bit of honor that is bestowed upon a chica who undertakes the role of slutty nurse for the night. Yes, most definitely.