con man
1. A man who exploits the vulnerability of others for his own sake by manipulating and taking advantage of their confidence (the act of which is known as a confidence trick or game). It is the common abbreviation of the full term, "confidence man." Be wary of con men who send e-mails claiming to be a bank or some other trustworthy establishment: they often ask for your personal bank details so as to have access to your finances.
2. By extension, a man who is skilled at duplicity, cajolery, or self-serving manipulation or persuasion. John is such a con man, always convincing others to pay for him on nights out under the pretense that he'll "pay them back later."