What we define as sexually arousing is so varied as to be difficult to put into words. However, the most arousing thing we humans have is our ability to think, to imagine and to feel.
Sex is not about touching genitalia. It is about getting aroused (and what you do with that arousal, of course).
The brain is where all sensation is integrated and perceived and where imagination, thinking and doing come together.
Orgasms exist entirely in your head. There is no neural reflex that will spontaneously produce an orgasm in a comatose or otherwise unconscious person, whereas it is entirely possible to have orgasms without any genital stimulation whatsoever. People with complete spinal transections resulting in their having no sensation in their genitals have reported experiencing orgasms.
Sex and seduction -- the premise of the sexy brain. Take good care of yours.