By the time they're old enough to laugh at each other's hair, they are the ones dictating the style - not mama or papa. Didn't say I dictated the style....but I do know how to keep a kid from being laughed at. My wife's parents had another son late in life, and then her father split....so I've been the father-like figure for him since he was 9. I usually know what's "in" and what's not "in" (more so with boys than girls).
Here's a little lesson...less reading, more TV. :)