ಠ_ಠ, the Look of Disapproval, is an emoticon usually used to express disapproval, disinterest, distaste or disbelief. It is usually used as a reaction to something offensive or inappropriate. Example: Person 1 says, "Hitler was a pretty cool guy." Person 2: "ಠ_ಠ"
According to Know Your Meme, this emoticon dates back to 2007. It was probably first used on 4chan (of course). Today, it is one of the more common text faces used on various online forums. You will find the Look of Disapproval all over Reddit, for instance.
The eyes of this face are created using the Kannada (language in India) Unicode character for ṭha, "ಠ". The mouth is just your standard underscore – "_". Put them together and you have a very disappointed face. ಠ_ಠ