The `Other Guys` actor kept the 13in latex appendage he used when he played porn star Dirk Diggler in `Boogie Nights` and has only just decided to store it away after previously keeping it to hand to play pranks on his pals.
He explained: "I used to keep it in my desk drawer. And I`d take it out and slap my friends in the face with it. I don`t keep many things from my movies, but that just seemed to have personal significance."
Despite his love of jokes, the 39-year-old star - who has four children, Ella, seven, Michael, four, Brendan, two, and nine-month-old Grace, with wife Rhea Durham - insists he has matured and is a much more sensible person nowadays.
He told the Times newspaper: "I`m only interested in being responsible, being on the level and not doing any dumb s**t."
Mark - who is now a devout Catholic - had a turbulent youth, getting into trouble for a string of petty crimes and drug abuse, but he tries not to regret the past.
He added: "All those things are the make-up of who I am. There are, of course, certain things I-d like to take away, or that I wouldn`t want to have to explain to my kids. But it`s all part of me.
"I`ve certainly asked forgiveness many times and we have a wonderful forgiving and compassionate God. But I can`t hold on to all the stuff I`ve done in the past. I`ve got to look to the future."