1. Your bedroom looks similar to this.
2. You believe you're: smarter, more creative, funnier than the average human.
Examples include but are not limited to: stopping mid-joke because you remember it's from Tumblr, and your non-Tumblr friend just wouldn't understand.
Let's face it the people of Tumblr do come up with some of the most artistic things on the internet, How many times have you added "Tumblr" to the end of a google search for unique ideas? Exactly.