Dealing with unwanted attention in the workplace is never fun. As you are keenly aware, it can indeed endanger an ongoing working relationship. It's important to remember, however, that this isn't something desirable you helped initiate, but something unwelcome to which you're forced to react. If you don't do something, it could escalate into a much bigger – and more contentious – problem.

There are several tactics you can try. When you have a chance, talk to this person in private. If you're already in a relationship with someone else and are quite happy, tell him so in a friendly but businesslike manner. If you're not involved – or simply don't want to establish an often verboten relationship with another employee – tell him, "I prefer to keep my personal relationships separate from my work," or "I never date within the company." If for any reason he becomes argumentative rather than acquiescent, cut off the conversation with, "I'm very sorry, but that's how I feel. I need you to stop approaching me this way." From then on, try to avoid any exchanges that he typically uses to make his romantic overtures.

But if he persists, seek the support of your supervisor and/or the human-resources department. Once you explain his uninvited advances despite your clear lack of interest, they will step in to formally bring his conduct to a quick close.