Definitions by Jon Ringo

bone smuggler 

someone who has sexual intercourse with someone else currently dating a third party.

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.

bone smuggler by Jon Ringo September 20, 2008