This is how I picture trolls who treat following back as an obligation
(APOLOGIES: It seems the images referenced in this post are not loading right now.)
Twitter is not Facebook. The “Follow” feature is not reciprocal.
Twitter is meant to be a meritocracy: If you have something interesting to say, people will follow you and retweet you, which should get you more followers, etc.
Which is why, from time to time, I get frustrated by apps that present their value proposition as “Find who doesn’t follow you and unfollow them immediately!” Taken to its conclusion, Twitter would be a sea of small clusters of all-following-all users, which defeats its point.
Then I found this gem:

I always check out my new followers

Jennifer followed me the other day and, like I always do with new followers, I looked at what she had to say. Sometimes the Twitter feed of a new follower doesn’t engage me, so I don’t follow them. Other times, I’ve found some very cool and interesting people, so I follow them. But I don’t feel an obligation out of politeness or custom to immediately follow someone who follows me. Like I said, meritocracy.
So when I checked out Jennifer’s feed, the above tweet was the most recent one. It made me immediately not want to follow her. (I can’t help but wonder if she went on a following spree and posted this tweet as a near-threat.)

Using the obligation to “follow back” to grow your followers

To claim following someone who follows you as “Basic Twitter etiquette” is absurd. It’s like two high school girls agreeing each can attend the other’s party, but neither girl really likes the other. So what’s the point? One might say “It’s all about numbers”, but that point of view ignores quality engagements.

Because they baited you with the follow, made you feel like you had to follow back, and then unfollowed you. It’s a dick move, but happens all the time.

But it’s a common tactic: Find users with similar interests as you, follow them, and hope they follow you back. It’s an easy way to get followers, especially those who are not hard-core Twitter users and might not understand its culture. So you follow a bunch of people and if they don’t follow you, you then unfollow them. And if you are especially Machiavellian, unfollow them even if they did follow you in order to keep your Twitter feed focused (unless you are a master at Lists).
Now, I don’t know Jennifer, and am speaking in general here and not about her specifically, but the claim that it’s “Basic Twitter etiquette” is bullying. People who take this approach are almost saying if you don’t follow someone back, you are doing Twitter wrong and a bad person. Like you’re making it worse for everyone else by not following the rules everyone else does.
But that’s bullshit.

My approach – value your followers and those you follow

I hold the opposite view. I have ~680 followers and follow ~330 users. Unlike Jennifer, who doesn’t care who you are, I do care about every single follower I have because I believe I have earned their follows. I wish these numbers were higher, but I hope all of my followers (are real and not a bot, and) find value in what I have to say about writing, social media, pop culture and what have you.
And I can tell you the reason why I chose to follow every single Twitter user I follow.
I could probably be a bit more aggressive in seeking out users I want to follow and hoping they follow back to drive up my numbers, but I have better things to do with my time… like complain about the Machiavellian strategies of some Twitter users.
So, bottom line: If you have something interesting to say on Twitter, I will follow you. But if you try to bully or shame me into following you back, it’s not going to work.