The obvious answer is Naked Boys Singing, and EQUUS is probably the most famous due to Daniel Radcliffe’s getting naked in the London and later Broadway productions. What are some others that feature “live on stage nekkid” scenes?
Some that I know of, though individual productions often opt to either use ‘nude suits’ or thongs or otherwise work around it:
Hair- usually in the ‘Be In’ song
Take Me Out- a comedy drama about a baseball player who comes out of the closet; features shower scenes. (The most surprising thing about this one is that I’ve seen a couple of college productions of it where the unpaid actors went full monty, speaking of-)
Full Monty (but only for a second at the end)
O Calcutta- there are pics of the 1970s production that feature a naked Bill Macy, later the husband ‘Walter’ on MAUDE. Really disturbing; some people you don’t wanna see nekkid.
What are some others?