Justin Bieber pulled a April Fools prank on Radio Disney. He was in studio to sing some songs, and after announcing "This is a song off my first album" his guitar player started playing, and he started singing the Miley Cyrus song Party in the USA.
The joke was ok, but I thought Justin could have went a little longer before saying "just kidding". It would have been funny if he would have sang the whole song and pretended that it was really one of his songs.