What does he mean by "It's one thing to be arrested"?

Native speaker’s answer
Rebecca
By "it's one thing to be arrested", he means that "being arrested" as a single activity is a big deal - or event. But by adding the fact that he was in a speedo makes it an even bigger deal. Ex: It's one thing to be late for school, but it's another thing to fail a class. Ex: It's one thing to start a business, it's another thing to actually succeed!