Tenure is not Heaven

One of our PhD program coordinators used to tell incoming PhD students:

"There are three reasons to be a professor: June, July, and August!"

He was implying that if you become a tenured professor you will have a lot of free time on your hands to do whatever you want.

I don't think this is true. If you become a tenured professor, you still have a lot of things to do, such as conducting/supervising research, committee work, teaching etc. Many tenured professors do manage to slack off (e.g. coming to work 3 times a week, taking the entire summer off, etc.). However, this is done at the expense of their responsibilities. Therefore, if you are a responsible person, I doubt you really have that much time on your hands to do whatever you want.