The requirements for the MTV Movie Awards' Best WTF Moment may be difficult to define, but they sure are fun to watch. Whether a flash of male genitalia, a pretty girl spewing black vomit or a cute old lady feeling up her soon-to-be in-law, this year's nominees had moviegoers scratching their heads, turning away in disgust or laughing out loud -- all fitting reactions to true WTF moments.

And if last year's winner, Amy Poehler in "Baby Mama" for "peeing in the sink," is any indication for who will take home the Golden Popcorn this Sunday, MTV viewers judge WTF to mean unbelievable.

Betty White in "The Proposal"

Betty White is so hot right now, she's going to be hard to beat ... even if the scene for which she was nominated features White feeling up Sandra Bullock during a wedding-dress fitting. If it had been anyone but the former Golden Girl, it could have been pretty awkward! White stole nearly every scene in the Bullock/ Ryan Reynolds rom-com.

Bill Murray in "Zombieland"

Spoiler alert for those who still haven't seen the film! The original Ghostbuster makes a surprise cameo so good, it was the highlight of the entire film. In the action/comedy, in which humans are trying to survive a Zombie takeover, Murray (who plays himself) gets the shock of his life when a group of survivors break into his house.

Isabel Lucas in "Transformers: Revenge of the Fallen"

Kissing scenes in movies normally go for the "sexy" or "sweet." Isabel Lucas' makeout with Shia LaBeouf in the blockbuster "Transformers" sequel was anything but. Particularly when her tongue was revealed to be more lizard than human, and she went in for the kill. Literally.

Ken Jeong in "The Hangover"

"The Hangover" was undoubtedly last summer's shiny cinematic gem of comedic brilliance. However, the moment when Ken Jeong's flamboyant and feisty Mr. Chow pops out of a trunk and lands on Bradley Cooper's face -- stark naked -- was way more WTF than laugh-out-loud.

Megan Fox in "Jennifer's Body"

She may be one of the hottest women on the planet, but in "Jennifer's Body," moviegoers saw an unexpected side of Fox. Particularly during the scene in which Fox's character is newly demonized and shown shoving food down her face. That was gross enough, until she started projectile-vomiting a stream of nasty black liquid.

Which WTF Moment are you rooting for? Tell us in the comments!

Don't miss the 2010 MTV Movie Awards, airing live from Los Angeles this Sunday, June 6, at 9 p.m. ET/PT.