In 2002, PSY was arrested for the possession of marijuana and as a result, was unable to attend his grandfather's funeral. During an interview, PSY remarked "I was very close to him. I was not there at the funeral. I will regret this [being arrested] for the rest of my life, because my grandpa loved me so much and I couldn't be there for him when he was on his deathbed."
PSY personally considers "Gangnam Style" to be the greatest achievement of his life.
source:wiki