being invisible means you can immerse yourself in a crowd and start clasping boobs and buttocks, then leap aside and laugh as some poor chap gets a clip round the ear. Laugh quietly obviously. And changing rooms! You can sneak into changing rooms and sit right there in the middle of the place while pretty girls get wet and take all their clothes off. You could go and hide in the showers themselves, but since the water on your body wouldn't be invisible you'd have to rely on them not noticing a semi-transparent man appear in the corner. You could pretend to be a novelty glass statue, but you wouldn't be able to explain the developing glass stiffy.