Hairdos and Don'ts for the Week of July 20

By Paige Ferrari

It's time once again for Wonderwall's examination of celebrity hair: where it can go right and where it can go terribly, horribly wrong.

Scarlett Johansson departs from her blond look, once again, with some questionable results.

Outside of comic book movies, fake red hair runs the risk of looking more Ronald McDonald than Julianne Moore. DON'T be afraid to go back to your roots once the "Iron Man 2" dye washes out, ScarJo.

Likewise, we'll always think of Katherine Heigl as a blonde, but this shorter, light brown DO is a nice change. Now if only we could find a way to make Izzie on "Grey's Anatomy" a little less vanilla.

Check out Rihanna's new spiky, forward-falling mohawk. No one else could pull it off, and it's probably handy for warding off invasive paparazzi and apologetic ex-boyfriends.

Just don't back your car up over Rihanna's DO, as tire puncture may result.

Anna Faris gets a lot of comic mileage out of Hollywood's dim-bulb-blond stereotype. Still, we DON'T like to see that the bleach is starting to leach its way into her brain.

Mickey Rourke doesn't seem to have any trouble with the ladies. Still, we DON'T understand how they stomach running their hands through his crowning glory: greasy blond dreadlocks, lightly perfumed with cigarette smoke and eau de crushed Oscar dreams.

Speaking of manes: if you're going to go for the teased-out hair-band look, DO like Dog the Bounty Hunter and go full out. Rock a perm with the big dogs, or stay on the porch.

Jennifer Lopez has perfected the act of peeking out from underneath her fringy brown DO, as if to say "What's up, Kim Kardashian? I was Hollywood's hottest butt while you were still in short pants."

Why must all sensitive young dude rockers insist on foresting their foreheads? We get what you're going for, Tyson Ritter of The All-American Rejects, we just DON'T think wispy man-bangs have staying power.

Remember in "Knocked Up," how Seth Rogen's character notes that Leslie Mann's character is lovable because her hair "always looks different"? Well, it does. Though we DON'T know if this business in the front, party-pony in the back is her best look.

We really wanted to believe that Demi Moore's mohawk was legit. (Almost as much as we wanted to believe that Britney was a virgin and Lindsay Lohan borrowed those coke pants.)

Sadly, this Photoshopped picture was Twittered by Ashton Kutcher in order to toy with our emotions. DO it for real, Demi? We loved your buzzed look in "G.I. Jane."

Well now, Shenae Grimes, aren't you the little lady? We DO like to see the "90210" star trade the shaggy SoCal high-schooler look for a little refined updo.

Unlike the ladies, Hollywood men don't get many opportunities to express themselves via creative hairstyles. This must be frustrating. Still, We DON'T like to see that Jonah Hill has chosen to update his look by cultivating some patchy chin grass.