Fat-bottomed girls make the world go ’round, and Lena Dunham knows it.

Lena Dunham absolutely hands Jimmy Fallon his “ass” trademark lip-sync battle on  Jimmy Fallon Live on Friday.

The Girls creator, 29, put in an enthusiastic performance of Queen’s Fat Bottomed Girls when she competed in a lip-sync battle with the late-night host.

Fallon, 40, is an experienced and highly effective lip-sync battler. It’s a brave guest who accepts the challenge.

At this move, Fallon said, “You can’t do that! I’m a father!”

Dunham, whose first song was Outside by her actual friends Calvin Harris and Ellie Goulding, clearly put some thought into her performance.

She was clad in a sporty ensemble to allow her “room to flex” and had devised some energetic choreography.

Watch the battle commence, below.

Fallon chose I’ve Never Been To Me by Charlene, an immensely cheesy ballad that allowed much scope for hilarity, and Run’s House by Run DMC. He was predictably awesome.

Dunham tweeted the video, commenting, “Lip sync battling my #1 teenage celebrity crush is now crossed off the to-do list. Luv ya.”

Man, if I could meet my #1 teenage celebrity crush, Drazic from Heartbreak High would be in so much trouble.