Bullying can happen to almost anyone. It's thought eight out of 10 children are bullied at some point in their lives.
Stars like world champion diver Tom Daley and Britain's Got Talent winner George Sampson have both been targeted by bullies in the past.
And JLS star Aston Merrygold and boxer Joe Calzaghe have also spoken out about their experiences at the hand of bullies when they were younger.
Cycling star Mark Cavendish told Newsround about how he was bullied at school - and got over it - in this clip.