It’s an internal response for me. It’s definitely a sexual turn on, and on some level I am thinking about how it would feel if we were intimate. It’s lovely to be able to run my hand down a man’s back and reach a firm butt. And it adds to the sensation of being close to each other because I can pull him close with a body part of his that is firm and delightful to the touch. To add to this, a firm body is attractive. I like to feel a firm body next to mine, to feel the contours of a man’s body. A great butt is a fine addition!