Happy birthday to YouTube, happy birthday to YouTube, happy birthday dear YouTube, happy birthday to YouTube.

It's hard to believe, but YouTube is a mere 5 years old today.

The domain name YouTube was registered on Feb. 14, 2005, but the site only went fully live on April 22. Since then it has served over 100 billion videos.

Sold to Google in 2006 for $1.65 billion, YouTube has gone from strength to strength, winning a small, Flash-based place in all our hearts. And to mark this grand occasion we've rounded up five of the funniest YouTube birthday videos. For a superhero party, tantrums and a head flambé, keep reading ...

Superhero birthday party

Party prank goes wrong

Awesome kid sings song then does awesome eyebrow dance. We're not familiar with the tune, but the description refers to it as a "birthday song," so who are we to argue?

Mad TV: Stewart's birthday

Birthday tantrum