When is it acceptable to get naked during Edinburgh Fringe

As a musician/performer... when is it acceptable to take your shirt off during a gig? 

According to a band we saw perform this afternoon in Edinburgh, the pre-requisites for taking your shirt off are as follows:

1. You must first ensure that you are not particularly physically fit.
2. You should wait until the crowd are ignoring the warblings of your one handed trumpet playing and are clearly as unexcited by the prospect of you taking your shirt off as you are excited by it.
3. You should wait until you've really done enough to earn it, or in this particular case, one minute into the first song of your strenuous half hour set.
4. You should not show any real sign of physical exertion, or indeed any particular reason to remove your shirt whatsoever.
5. The removal of your shirt should ideally be accompanied by several raised eyebrows, a scattering of confused looks and a chorus of whispered "put it back on".

That being said, we applaud the individuality of those performers who choose to remove their shirts for no particular reason. 

It is the Edinburgh Fringe Festival after all. And isn't unwarranted shirt removal really what the Fringe is all about?