A Very Supernatural Christmas [gifset] - Dean's expression in the bottom right frame--a split second of realizing what "the life" has cost Sam; what he himself has taken from Sam in the way of a childhood, and Dean doesn't feel good about it.
THIS moment killed me. I called my sister right after crying. There is no bond like the one between siblings whether it's brother/sister, sister/sister, or brother/brother. I couldn't live without my sister.