My wife uses "sexy" to describe certain guns & cars. In her words, if something looks exciting (but not sexually exciting, that would be weird), then it's sexy.
It's also contextual. Let's look at movies:
A WWII-era gun in Indiana Jone's calloused hands? Sexy.
The single action-esque gun used by Mal from Firefly is sexy. The same gun in Jayne's hands would become thug-like or outlawish.
A gun in Doctor Who's hands would be rediculous; he's a thinker, so what would he do with it?
007's guns would be harder to describe. Words like "quaint" and "genteel" come to mind, but not "sexy". Edit: I don't like the latest 007 because he's too harsh & brutish. Likewise, any gun in his hands becomes a tool.
...on the other hand, there might be something Freudian about guns being sexy or not; my wife likes guns with loooong barrels, while I like snubs with a big hole on the end. I prefer to think of this as coincidence.