Person on Tumblr: FUCK YOU. I HATE YOU. JUST LEAVE.
Translation: You are wonderful. Something that you have just done is wonderful. I love what you do/are/said/etc. Please continue in this fashion.
Person on Tumblr: HJAIOERJTIOASJFIOASD WI3ROKJIOADSF IOAEJIOKJA!!!!!
Translation: This makes me extremely emotional. Most likely in a positive sense.
Person on Tumblr: WHAT IS YOUR FACE. I CAN'T EVEN.
Translation: You are a very attractive individual. Congratulations.
Person on Tumblr: THAT'S IT. I QUIT.
Translation: You are very talented in your given endeavor (photoshopping/fic-writing, etc). Sometimes I wonder if I could ever achieve that level of skill. Please continue what you're doing; you are an inspiration.
Person on Tumblr: I want to have sex with you.
Translation: I want to have sex with you.