AKA, Stop Doing Something Illegal Day
Well, this one is rather wide open, isn't it? Hopefully virtually everything you're already doing is legal.
If it's not, stop it! Just stop it!
You might consider targeting especially the kind of things that have laws associated with them.
For example, there are those things called Speed Limit signs along the roads and streets and highways. Actually, I bet this is one thing that you do illegally almost every day - driving over the speed limit.
Everyone does it, right? You have to keep up with the traffic, right? You're good at rationalizing, right?
Maybe today, to celebrate Do Something Legal Day, you stay in the right lane (on multiple-lane avenues) and try not going over the limit. You might be surprised to find that you get to your destination about the same time as usual.
If you don't drive at all today, just get along with your legal self, as if there's nothing to see here. Have a happy March 16.