I used the term to refer to non-hispanics while I was down there, since I was focusing on getting as much interaction with native Spanish-speakers. There's especially A LOT of study abroad kids from the US and Europe that like to pregame at Sugar before walking over to the boliches in Palermo.
I never really found too many good happy-hour spots that weren't full of foreigners. I would mostly go to them just to get a decent beer in the late afternoon (Gibraltar, Antares).
I think it's pretty fun to go out in places like Flores, San Cristobal, Ramos Mejía, etc. Those places have the hardcore, gritty argentine nightlife, and 10 peso liters of beer, 1 liter plastic cups of fernet & coke, etc. You'll also see things out there that you'll never see in places like Palermo and Recoleta.