I'd be happy to get a snort, or a wave, or a howdy. A wolf whistle would probably shock the heck out of me. I don't get those. I think I posted a while back about a friend who is a UPS driver whistling at me when she drove by, and I didn't even realize she was whistling at ME until she called my cell.

I wave or nod at bikes, and always wave/nod/mouth "thank you" to cars who give me right-of-way, even if I had right-of-way anyway.

I doubt that in my case the cars were nice because they could look up my skort or see my pretty gams. More likely they thought, "Oh, jeez, look at that poor woman trying to ride a bike. Better give her some room."

(though I'd like to think they were admiring something... at least the bike!)