When I first came to NYC I rigidly ignored all of the random people (men) on the street who would holla ( "hi!" "hey beautiful," "you're so beautiful," *whistle* etc) at me. But over the years I've loosened up, and at least offer a smile or nod in return. I'm one of the few people I know in Manhattan who doesn't ignore any and all attempts at transient communication from the locals and tourists.
But I really can't stand the people in NYC who wait a split second after you pass them to holla at you or whistle, because at that point of walking past them you can't really acknowledge them and just keep walking. So it turns into having some perverted coward scream at your back and not really being able to turn around because that's just awkward. And its not like you can individually yell at them for being cowardly because the next day someone is going to do the same thing. :[