My wife thinks guns can be sexy. She likes either snubbie revolvers that they used in old detective movies, or long single-actions that you see in some westerns. I think it's mostly an image thing; to her a gun is sexy because it goes with the movie role.
Personally, the closest I come to this is having an appreciation for tough handguns or sleek rifles. Maybe just I haven't seen the right gun on the right leading lady.
I can think of several firearms that I find aesthetically pleasing to my eye...a stainless Colt Python. A stainless Beretta 92. A Ruger Vaquero in the factory high-gloss stainless finish. The list goes on. But, I tend to be somewhat literal in my thinking. Therefore, to me, "sexy" is interpreted as "something that makes me think about and/or desire sexual intimacy". With that said, my answer to this question is: "HECK, NO!!"
No most guns are not sexy.
I remember a scene in the popular 1980s legal drama; LA Law, where a series regular(played by Susan Dey) had a stalker or some whacko making threats. She goes into a LA area gun shop and some scum-bag "Hollywood stereotype" sales clerk shows her a stainless model Walther PPK .380acp and seeps; "Sexy, isn't it?"
Even as a young kid, that TV scene made me cringe.