What are the negative consequences of slacking off after attaining tenure?

As I was thinking about the question Can I slack off and get a PhD?, I realized that I wanted to say in my answer

If you want to slack off, the best time to do so is after you have received tenure as a college professor, because at that point you can't be fired except for egregious offences.

I am not yet even an assistant professor, so I don't know whether the statement above is really true.

Question: What could the negative consequences be for a professor who has just received tenure, if he were to put in the bare minimum effort needed in teaching just to achieve average teaching performance, and were to just stop doing research and publishing papers?

Note: I don't plan to slack off if I were in the future able to get a tenured position, but I am just curious what happens to those professors who do.