These guys are really nailing it!

Several of Hollywood's leading men have been curiously busting out nail polish and painting only one finger. The reason, though, has nothing to do with vanity and everything to do with righting a wrong.

A new viral campaign by YGAP -- called "Polished Man" -- is underway to get men to paint one single nail with a color of their choice to raise awareness about ending physical or sexual violence against children (think of it as the new push-up challenge).

One of the first to give his finger some color was Chris Hemsworth.

"I just signed up to the @YGAP @polishedman campaign! One in five children fall victim to physical and/or sexual violence, before they turn 18. That's one too many. For the month of October, I'll be painting one nail to represent this statistic and raise awareness and funds to end violence against children."

He encouraged others to sign up and donate to the campaign that has raised over $500,000.

He later shared another snap sporting a red shade on his pointer finger, saying, the campaign "isn't just about remembering to buy flowers, how many rounds you shout, or how much you lift. It's about saying no to violence against children."

He later challenged his brother Liam Hemsworth, Zac Efron, Robert Downey Jr., Jeremy Renner, Mark Ruffalo and Tom Hiddleston to participate. Several of them obliged.

Liam went with a lime green hue.

"Thanks @chrishemsworth happy to also be a @polishedman and paint a nail this month to say NO to violence against children," he said. He then nominated Jimmy Fallon and others to support the cause.

Zac jumped aboard, as well, going with a red color. He went on to challenge James Marsden, Hugh Jackman and Adam Devine.

"Suits" star Gabriel Macht also got in on the action.

According to the causes' description, being a Polished Man "means you don't turn your back on the vulnerable. You raise your voice—and nail—to say, 'not on my watch'. You embrace the smirks and know it doesn't matter; there are worse things than being embarrassed by a little mani."

The nail polish idea was inspired by a little girl who had been repeatedly physically and sexually assaulted in the orphanage where she lived, the Polished Man website says. After meeting YGAP CEO Elliot Costello, the little girl painted his nail and said goodbye. Elliot continued to paint one nail to remember her.