I've had a variety of reactions from various Argentines related to my being an estadounidense, but I don't know that I would classify it as racism. How I'm treated, even by people who don't like estadounidenses, doesn't compare, for example, how I've seen my Paraguayan family members treated at times.
I get three basic different reactions when I answer an Argentine's inquiry as to where I come from.. 1) Oh, how nice, i.e., general pleasantness and good conversation (which I love, because I really don't like conflict and like talking to people), 2) An obvious feeling of either envy or anger, not necessarily directed at me personally (at which point I try to extricate myself from contact as quickly as I can without being rude) and 3) Telling me how good the US is and how bad Argentina is (not a common reaction, but probably more common than #2 - and I don't feel all that comfortable with #3's reaction). #3 usually includes things like "why on Earth are you living here??"
I've had one single encounter in the 9 years I've lived here that was verbally violent and nearly physically so, in the vein of #2. I was in Café Iberia a few years ago with some expat friends. We'd stopped in there for coffee after a dinner at Plaza Asturias. We were up on the second floor of the place, sitting in the couches near the railing, having a calm chat. A guy at a table across the aisle, against the back wall, who was seated with his girlfriend, kept looking over at us. He was a big, burly guy (rugby player I found out during the better parts of our later "conversation"). He started throwing some comments our way, which didn't seem at all provocative at the beginning, asked us where we were from, what we were doing here, etc. Then he started talking about the greatness of "la patria Argentina" in a rather forceful manner, as if we were arguing with him. Since I was the only one of our group of four who spoke decent Spanish at the time, I was doing most of the conversing on our part and was very careful not to give any attitude. Had nothing to do with the dude's size, but rather I was very cognizant that I was in a foreign country and didn't want any trouble, though I felt trouble coming when he got up from the table and started conversing with us from his vantage point of standing over us while we were seated. I could see that something was bothering him.
His girlfriend ended up walking over and throwing out rude comments about where we were from, then leaving and going back to her table to sit down, then coming back again, etc. She seemed to act as some kind of a macho-catalyst and the guy got to the point where he actually told me he was tired of hearing our filthy language, polluting "his" space in his country, amongst many other direct insults. He ended up demanding that we leave Iberia immediately. I'd finally had enough of this guy's crap, so I stood up in front of him and asked him if he had a problem that he would like to go outside and resolve so we didn't continue to ruin the rest of the night for everyone else. He looked at me for a moment, had a few last-gasp insults to throw out and went to sit down again with his girlfriend and we didn't have any more trouble.
Like I say, that's the only direct real issue I've had in 9 years here. Not a bad track record. I don't think it's racism when people come out as anti-American as much as it is a mixture of envy, anger based on mostly bad propaganda and a feeling of inferiority related to wanting to feel that Argentina should be better than it is.