I suspect that it may be a common Asexual experience but when I imagine something as "sexy", I imagine something that makes your heart beat fast, that gives you goosebumps, that captures all your focus and puts a hitch in your breath and an odd tingle on the back of your neck, that is exciting and enjoyable to think about.
By extension, things that I believe are "sexy" include:
More magpie pictures, because not only do they have black trousers, they also have absolute shiny details on their wing and tail feathers - such beautiful birds.
Rhododendron and Bombus ternarius (orange-belted bumblebee)
I'm walking by a white rhododendron when I hear a buzzing sound. Sure enough, out pops this bumblebee and then it's straight on to the next flower. Bumblebees are the heavy lifters of the flying insect world. They can double their body weight tanking up on nectar and can carry half their weight in pollen. To accomplish this, they beat their wings an incredible two hundred times a second. This is peak season for rhododendrons and this particular orange-belted bumblebee is obviously making the most of it.
Remembering the one Hades and Persephone fanfic retelling I read where the author had clearly never eaten a pomegranate in their life and just had the character in the Persephone role take a bite out of the side like an apple