The track spends a fifth week at the summit, keeping Rihanna's 'We Found Love' at number two, while Maroon 5 and Christina Aguilera's 'Moves Like Jagger' completes the top three.
Elsewhere in the top ten, Ed Sheeran's 'The A Team' vaults from 13 to five, while David Guetta and Usher's 'Without You' advances from 11 to six.
Further down the chart, Jessica Mauboy and Stan Walker's 'Galaxy' leaps from 28 to 13, while Lloyd, Andre 3000 and Lil Wayne's jump 32 to 14 with 'Dedication To My Ex (Miss That)'.
Snoop Dogg, Wiz Khalifa and Bruno Mars debut at 17 with 'Young, Wild & Free', Taio Cruz and Flo Rida's 'Hangover' climbs from 27 to 19, and Ricki-Lee's 'Raining Diamonds' lands at 23.
Meanwhile, Christina Perri's 'A Thousand Years' starts at 34, and Jason Derulo's 'Breathing' enters at 36.
The Top 10 singles in full (click where possible for our reviews):
1. (1) LMFAO: 'Sexy And I Know It'
2. (2) Rihanna ft. Calvin Harris: 'We Found Love'
3. (3) Maroon 5 ft. Christina Aguilera: 'Moves Like Jagger'
4. (4) Flo Rida: 'Good Feeling'
5. (13) Ed Sheeran: 'The A Team'
6. (11) David Guetta ft. Usher: 'Without You'
7. (10) Calvin Harris: 'Feel So Close'
8. (8) Foster The People: 'Pumped Up Kicks'
9. (5) Gym Class Heroes ft. Adam Levine: 'Stereo Hearts'
10. (7) David Guetta ft. Sia: 'Titanium'
Watch LMFAO's 'Sexy And I Know It' music video below: