The pair joined the panel of the pop star search show this year and Demi revealed they quickly bonded over ''tic tac toe and doodle''.
The 'Skyscraper' singer said: ''We bonded at 'The X Factor's boot camp. During breaks we'd sit behind the panel and use the paper to play tic tac toe and doodle.''
Demi also revealed she loves to play pranks on her staff.
She told People magazine: ''I do Little Ones all the time. When my make-up artist is going my makeup, I like to scare her when she is really focused. I jump back in my chair and she freaks out. It's actually not very smart because it can totally mess up what she's doing.''
While Demi spent time in rehab in the past for emotional issues which included dealing with her body image, she is now healthy and happy and loves exercising.
She said: ''I go running on the beach and then I do a little meditation afterwards and put my feet in the water.''