Q: What do lawyers wear to court?
A: Lawsuits!

Explanation: There are many, many lawyer jokes; this is just one example.

Lawyers go to court to represent plaintiffs (civil court), defendants (civil court and criminal court) and the prosecution (criminal court).  When lawyers go to court they need to wear nice clothing- usually they wear a suit because it is a formal situation.

A lawsuit is when one party sues another in court.

This joke plays with the words suit and lawsuit: the idea that a lawyer who works with the law would wear a law-suit.

Here is one of my favorite law videos: How a bill becomes a law.