lurking troll

A person who subscribes or follows a feed because it is so stupid that it makes them feel smart.

Unlike other trolls, a lurking troll won't vocalize their opinions.

Dan: Wow I got 5 new followers on twitter! I should keep making hilarious cat puns!
Dick: I don't know Dan, I bet most of them are giving you a mutual follow or are lurking trolls. Your life is pretty sad
Dan: *Cries*