Hi Aaron,
If you are having some specialized qualities, which have good values, in the industry circle, e.g. in shipping industry, people attending Customs jobs efficiently, or in Pharma industry, good MRs who have good contacts with Doctors, most of these type of people are known in similar companies by their names, personal style of work, attitude etc. If such person decides to change his job, it becomes news for all other related Companies. Also when Executives, with higher positions, think of changing jobs, it becomes news, and if they play any mischief, it is troublesome for all concerned.
If you feel, you fall in such kind of category, then to some extent, HR, who is now annoyed, because of your backing out, may spread bad words about you. Since you have backed out at 11th hour, which is certainly not a good thing, anybody will become uncomfortable, and will think of teaching you a lesson.
Ofcourse, such kind of thinking /attitude, (Yours as well HRs), is totally unprofessional, and nobody should actually behave like this. I am 100 percent sure the concerned HR has just threatened you to make you frightened, and in reality will not behave what he has said. This is a temporary anger, and he will forget the issue, once little time passes away, and once he becomes active in selection of another candidate of your designation, and also sees another equally competent person, like you. Even he may give you a big thank you, if you meet him coincidently, on any occasion, or suddenly in travel, and will say, ‘Good that you didn’t join, I got much much better person, and my bosses have given me appreciation for my Excellent job of selection of perfect candidate’. (These will be ofcourse his sarcastic remarks, to make you uncomfortable).
To conclude, I don’t think, in whatever capacity, the person is working, no HR can spoil anybody’s career by such kind of tacties. So Relax !
Suggestion : Meet the annoyed HR personally, very politely give some good reasons, for your backing out, which should sound genuine. Apologise and say Sorry (again it should sound genuine, and from bottom of your heart). I am sure, if at all he is planning to disturb your Career, he will become cool.