First and foremost: you are responsible for your own safety, including making sensible clothing choices, and adjusting appropriately. If it looks like it might hurt, you're right--it might! Fortunately, most discomfort and injury can be avoided with a little foresight.
What constitutes a sensible clothing choice? Most often, one of these: http://en.wikipedia.org/wiki/Dance_belt If you don't own a dance belt, you can find one online or at a local dance supply. Like underwear, they're sized by waist measurement. Speaking of underwear: if you don't have a dance belt, you can sometimes get by with briefs. The tighter, the better. Anything with loose legs (boxers, boxer briefs) is almost certainly a bad idea.
What constitutes an appropriate adjustment? Almost always, "centered high in front." More generally, "out of harm's way," where harm can come from a fabric wrap around the leg, or from straddling a trapeze bar, or from folding at the waist and hanging on any apparatus.
What does it mean to be responsible for this? It means paying attention, both to what your eyes see (potential harm), and to what your body tells you ("hey! this isn't comfortable!"). Often, it means making discreet adjustments during class.