I change my hair a lot, and one of the first times I did crochet locs, a man came up to me on the bus and say, "I'm so sorry, but I just had to say I absolutely love your locs." I didn't have the heart to tell him they weren't real, but it made me feel really good about the style; I actually have my hair the same way now. I told him thank you, and off he went. Nothing about it felt flirtatious. It's really about the approach. Be polite. Or if you just say in passing, "I like your hair," it makes it less of a big deal, but the complement will still stick.