The email clearly states "using our trademark and CONTENT". That's what the email is for. Furthermore, their TOS is worded to be confusing (at least it is to me): http://9gag.com/tos
Anyhow, I'm not going to make this into im-a-bitter-dev commotion. Some here even state that it's not the users I'm worried about because if I am, then I can just direct them to the official app.
My real concern is that my app existed before 9GAG's, and although 90% of my users are using it free, there are some who appreciate the work I put into making a nice-to-use app and bought the "Pro" version. These are the people I would NOT want to disappoint. I'm still weighing solutions and brainstorming on how to make their dollar spent worth it. But for now, I've removed 9GAG references in the Play Store listings.