I used to dive bare belly but got one mighty fine fire coral hit in KL one year. That thing weeped fluid for a couple months. I always got fire coral hits, but this one was a real dandy. (Did I mention..fire coral hurts?)
Then I dove long sleve shirts and dockers pants. Found I needed suspenders to keep the pants up. There is more drag when wearing street clothes underwater. People look at you kind of funny too.
Started wearing a 2/3mm, surfer style $50 wetsuit. Makes me feel like a wuss but when I need to straddle a tube, horseback style, in current, on an oil rig and knife a struggling fish I'm a lot more comfortable about gripping the rig with my legs when I have some neoprene and fabric between my skin and the stinging stuff. Did it with dockers and bare skin for a long time too, but like neoprene better.