I found myself very lucky to come home from a series of interviews with 4 job offers from 4 different groups within the same institution. Without making this personal, the institute is focused on collaborative research so these groups all work closely together and often interact on a day-to-day basis.
In any race there has to be a winner, but it was incredibly difficult to choose; I value each group and their respective approaches to their science greatly. In the end I chose the job that seemed to fit my career goals the best and the supervisor that I felt I would get along best with.
Since my decision was made and upon starting my new job, I have run into one of the supervisors, whose job offer I turned down, roughly twice a week. In each of these interactions, he makes some snide comment about me not taking his job offer - it is literally the only thing he can think of to say to me during our brief conversations. I respect this man for the wonderful scientist that he is but I'm frequently frustrated by these interactions, and I can't go on like this.
How do I help him recognize that he's harping on this issue, and how do I remain steadfast as he tries to make me feel like I made a bad choice?