Referring to a gay, bisexual person, a person who likes anal.
Bone Smuggling is the art of a BONER being Smuggled into the rear of another being. Therefore, Smuggling the bone(r).
Guy: Hmm, I'm a Bone Smuggler
Girl: Aiii PAPI!!! Smuggle that bone all you want!
So if Bridget and Robert are dating and Bridget and Marty are boning, then Marty is the smuggler, Brigdet is the smugglee, and Robert is getting smuggled. Marty is bone smuggler.