|You expressed your concerns to the president, and he expressed his lack of concern to you. The decision appears to be made.|
However, since you are so upset over the possibility of this individual joining the company, you should meet with the president again. This would not be a time to merely repeat yourself, wave your hands, or stamp your feet. You need additional data.
One step is to take some job-related references on this individual and conduct any additional checks that you use with other applicants for this type of position. Obviously, if you uncover any compelling information that could throw up a red flag, this is something to wave in front of the president. If you come up with nothing in checking out this applicant, you have no choice but to hire.
In such a scenario, try to keep your expectations positive. In spite of his preemployment antics, you might be surprised. However, if this individual's performance is marginal, use appropriate coaching and documentation, and keep the company president advised. Hopefully the president's performance on this matter will not be marginal.