One of the more flamboyant people you know is suddenly acting a lot more conservatively and it's piquing your curiosity big time. Their change in behavior could be because of a new job, a new problem, or a new relationship: and you need to find out what the deal is today before it drives you crazy. Shoot them a text or email that casually asks them 'what's up' and then take it from there. Make sure they know that while you might miss their old ways, you'll always support the path they take.