I've always thought it would be interesting to allow as a defense against a violation of a law to prove that the law is regularly violated without consequence.
Because selectively enforced laws are just another way of saying you have a king at some level, the person who decides to enforce or not.
Selective prosecution is a defense under the Equal Protection clause of the Constitution.
However, the Supreme Court has left the prescribed remedy intentionally vague since 1996, which in turn makes the claims themselves less likely to be raised, and less likely to succeed.
Has a lemonade stand violation ever resulted in a jury trial in the US? I'm skeptical. In places that enforce those rules, usually what happens is that the cops tell the parent it isn't allowed, the kid shuts it down and there's no fine.
Because selectively enforced laws are just another way of saying you have a king at some level, the person who decides to enforce or not.