Lady Gaga over the moon at MTV Music Awards
The singer, 25, was unrecognisable underneath a mask-like hat and giant silver disc worn to collect the Best Female award at the Belfast ceremony.
She joked: "I'm really smiling right now I know you can't tell. I've had a lot of Botox."
She also made a gag about David Hasselhoff's manhood as he presented her with the award.
Replying to an earlier joke by the Baywatch star - who claimed to have drilled a hole in his dressing room wall - she praised his "big p****."
The Hoff joked: "All the nominees are very beautiful women. In fact there are a lot of beautiful women backstage in the dressing room next to me.
"In fact, I drilled a hole in the wall in case they want to watch me changing."
And Gaga took the gag a little further, telling him: "I'm in the dressing room next to you and you have a very big p****."
Later the Poker Face diva showed some cheek flashing her rear at the end of a performance dressed inside what looked like a giant POPPY.
She wore the red costume to sing new song Marry The Night on top of a huge cratered moon.
Rocking the show ... Lady Gaga
GaGa also won Best Song for Born This Way, plus gongs for Best Video presented by model Bar Refaeli, 26 and for best fans.
Collecting the song award, GaGa said: "I knew that this was very special when I wrote it, and I didn't know when I first started out as a songwriter how special it would be. It's the most important single to me."
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POKER Face star reveals her behind at MTV awards bash in Belfast
Katy Perry picked up the first award at the European Music Awards, and praised her fans' 'commitment'.
The Firework singer beat Lady Gaga, Coldplay, The Red Hot Chilli Peppers and Foo Fighters to be named Best Live Act.
Best Live Act ... Katy Perry
She said: "It's easy to buy a song, download a song, steal a song. But to buy a ticket and see an act live is real commitment."
And she added: "I'm so tired, but it's been worth it."
She also presented the Global Icon award to Queen.
Video: Gaga jokes about Hoff's manhood
MTV EMA winner praises Baywatch star's big p*** after dressing room gag
British rockers Coldplay had opened the show at the Odyssey Arena with Every Teardrop Is A Waterfall. Katy Perry and Justin Bieber also performed.
Earlier Coldplay frontman Chris Martin, 34, said he was a Justin fan confessing: "Even I've got Bieber fever."
Putting the disc in disco ... Lady Gaga
Hordes of teenage girls spent the weekend camped outside the 17-year-old's hotel in the centre of Belfast in the hope of glimpsing the Canadian singer.
The teen took two awards for Best Pop and Best Male. Bieber's actress girlfriend Selena Gomez, 19, hosted the bash presenting one section wreathed in a ring of FLAMES at the spectacular do. She also managed a series of quickfire costume changes.
Video: Best of the MTV EMAs 2011
WATCH highlights of best performances from music awards show in Belfast
Justin made a veiled reference to allegations that he fathered a fan's baby as he picked up the Best Pop honour.
He said: "There's been a lot of c*** on the internet lately but I've pulled through it. Thanks to MTV."
He made no mention of hostess and girlfriend Selena Gomez as he collected the Best Male Artist gong.
He said: "I voted for Kanye West but whatever. I want to say thank you to all my fans and my family. You guys are the reason I'm on stage today."
Best Male ... Justin Bieber
Bruno Mars was named Best New Artist, beating Jessie J, Far East Movement, LMFAO and Wiz Khalifa.
And he told the crowd, "Follow your dreams."
Then he added: "I shouldn't have said that. That was corny."
Queen were Britain's only winners, picking up the Global Icon prize.
The group closed the bash with two classics We Will Rock You and We Are The Champions. Former American Idol runner-up Adam Lambert sang in place of late frontman Freddie Mercury.
And Amy Winehouse, who died in July aged 27, was remembered in an emotional video tribute by fellow former Brit School pupil Jessie J. The Essex singer, 23, told the crowd: "She inspired so many of us."
Before the do, artists had been given a list of Irish words to learn and had beef and Guinness stew for lunch.
Stars also took home goody bags worth an estimated 10,000 which included games consoles, jewellery and Irish whiskey.