Although I tried to stay away from this thread as it's a subject too dear
to my heart, I can't abstain any longer.  The most obvious sexuality in any
classical work, for me, is Bantock's Sappho for solo voice and orchestra;
sex almost drips off the audio equipment.

When sex is obvious in music, that's fine, but what's even better is
finding sexuality in works where it is not generally noted or known.
Of course, the "listener" plays a large part in this process.  He/she
might feel sexuality from a piece of music although the composer had
no such feeling to convey.  I find the Art of Fugue loaded with sexual
imagery; that's probably just me.  The same goes for the WTC - both books.
Beethoven's string quartet opus 95 is in the same category as is the first
movement of Mozart's piano concerto no. 24.  Also, many of Bach's organ
works convey to me a sexuality of a macabre and powerful nature.  There
are many more, but I'm just indicating that I most appreciate sexuality
in music when I feel it from works that do not display it on the surface.

Don Satz