Participant Researcher

I suppose my reaction would be dependent on how close I was to the person. If I was not close to the researcher, or only knew them as an acquaintance my reaction would probably be pretty mild. I might think, "huh, didn't expect that", or "wow they don't seem like a researcher". However if I was close to this person, like a good friend or room mate then I would most definitely be offended. It would feel like I was lied to or betrayed, and I would probably doubt the sincerity of all their actions thinking, "this could all just be an act so they can study me".

The nature of their research would also play a part in my reaction. If they were simply researching something like, how freshmen deal with their first year in college I would probably not be THAT offended (this of course is dependent on how well I know them). But if their study was something like, The Increase in ignorance and Laziness of Freshmen I would definitely be bothered by their work. I would also feel cautious and offended if they were unwilling to divulge the topic of their research.