From Axenome:

Catcalls and whistles... it amazes me how women can take offense to this -- it isn't meant to be degrading -- it's a show of "guy" admiration. Guys are simple beings with simple responses. We aren't all that complicated. If we see something we approve of or someone we find to be attractive, we'll say it. Or whistle. It's not an insult, it's a compliment.

From Hannah:

I fail to see what is sooo horrible about a guy honking or whistling at a girl. It's a compliment, not a insult. They are saying you look hot today. What's so bad about that? I usually wave or curtsy, they smile, and we both go about our business. I really don't see the insult in all that.