Michael Douglas has learned over the years to let some comments slide. The 76-year-old Oscar-winner was recently mistaken for his 18-year-old daughter's grandfather at her high school graduation and the star didn't let the remark cut him too deep. Douglas recalled the experience while appearing Monday on "The Kelly Clarkson Show." "I gotta tell you Kelly, it's a little rough when you're going out the doors and the other parents are saying, 'Oh congratulations…you must be so proud of your