People who do such a thing are perfectly idiotic. I mean, come on! Are you seriously not confident enough to get your fans through your own merit? If others want to be your fans, they'll do it. Asking them to add you or threatening them is plain stupidity.
In my case, I don't go asking for fans. In fact it's almost the opposite: I'm not even hoping anyone would add me. If they want to, I say go ahead, and I'll add you back in return. I bet those who ask you to add them don't add you back anyway.
The people who ask to add them I guess, since I know the people who threaten to report you are full of sh*t since that'd be impossible for them to do... xD