I have traveled several times to buenos aires by myself & I have never had any problems walking around alone. Just take the same precautions you would in any big city - don't wear expensive jewelry, don't flash a lot of money, don't walk down dark streets by yourself... If you use common sense you'll be fine. And FWIW, I don't look Argentine at all & people know I'm foreign & again, I have never had any problems.
Argentine men do tend to talk to you but it's never threatening - enjoy the admiration