Quillifer by Walter Jon Williams

Quillifer is a silver-tongued law student who has a penchant for talking himself out of, or more often into, all sorts of scrapes and predicaments. At first he is concerned with little more than getting into and then out of the chambers of the latest girl to strike his fancy. Then his town is sacked, and he must accept a new life, even becoming a soldier and a sailor. Even here, he employs his charm more than his sword, though he does find that you disappoint a goddess who you have charmed at your own peril.