Calo thought being invisble sucked.
He was sick of people thinking he was a stinking ghost. He wished he could of not chose to be invisible that day.
That day was when he found a genie. The three wishes mumbo jumbo, The only problem was the wishes couldn't be reversed.
So now Calo spent his time floating around his school, scaring the living daylights out of the smokers behind the bike shed, or frightening year 7's by slamming doors in their faces.