Someone said it first, but I agree; when something makes you think of an attribute that you, personally, find sexy then that object is sexy to you.
When I lived in the country, a lot of women said pickup trucks were sexy. They did not want to rub themselves on a truck .. they wanted a man who was rugged and strong and outdoors-type.
I suppose women who say sports cars are sexy could want a few things. Cheap and dirty sports cars like a Mustang prolly feels like a bad-boy ... where an Aston Martin reeks of money and power.
Sexy is whatever turns you on. Thin people, fat people, strong people, needy people ... everyone has a turn-on