Those baby blues, the pearly whites, the oh-so-kissable lips -- Zac Efron proves a triple threat when it comes to flashing a grin. On Sunday night (April 13), his smile was on display to knee-buckling effect -- [article id="1726052"]second only to his abs[/article] -- upon winning Best Shirtless Performance.

Here are six of our favorite sexy smirks by the "Neighbors" star, from the red carpet to acceptance high jinks to backstage at this year's MTV Movie Awards.

1) Crooked half-grin with a side of flexed biceps, please! Efron's first appearance at the Movie Awards, via the red carpet, left us fanning ourselves. We just want to muss up that spiked hair, and the way that denim T-shirt hugs his arms? Swoon! The lopsided expression just adds to the charm -- that's a smile complete with killer accessories!

2) Apatow-tastic! We give this backstage Zefron grin a thumb's up -- especially considering the fact that funnyman Judd Apatow is on Zac's arm. To be a fly on the wall for the conversation moments before this photo was snapped! Note to Judd: Your next film could use 100 percent more Efron!

3) Let 'er rip! Rita Ora is our new BFF after taking it upon herself to interrupt Efron's winning Best Shirtless Performance speech by tearing open his denim shirt. And we're definitely not complaining! Is it hot in here, or is it just Zac?

4) Smile? What smile? We're a little distracted. ... So you thought we'd only post one Best Shirtless Performance-winning money shot? Ye of little faith! We can't stop staring at this photo of Efron shortly after he shrugged out of his top.

5) Zefron sandwich! Flanked by two appropriately adoring ladies -- Jessica Alba and our new favorite shirt-ripper Rita Ora -- Efron is in no rush to cover up backstage.

6) Would you like butter on that? We're matching Efron's mile-wide grin thanks to all the flexing going on in this shot. That statuette looks mighty heavy, Zac -- we'd lend some help, but we're mesmerized by watching you shoulder it!

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