I've been rewatching TOS recently, and I noticed that Chekov's hair had a mind of its own for a while. I took a few screenshots, looked up the story behind it, and made this really quick for anyone like me who wasn't aware.
Roddenberry wanted Chekov to bring in the youth audience, so they gave him a wig to try to make him look like he's from the Monkees or the Beatles... absolutely hilarious.
Boy bands throughout history have made careers based on the fact that 12 year olds care about their haircut.