The criterion of embarrassment, also known as the "criterion of dissimilarity", is an analytical tool that Biblical scholars use in assessing whether the New Testament accounts of Jesus' actions and words are historically accurate. Simply put, trust the embarrassing material. If something is awkward for an author to say and he does anyway, it is more likely to be true.http://en.m.wikipedia.org/wiki/Biblical_criticism
The essence of the criterion of embarrassment is that the Early Church would hardly have gone out of its way to "create" or "falsify" historical material that only embarrassed its author or weakened its position in arguments with opponents. Rather, embarrassing material coming from Jesus would naturally be either suppressed or softened in later stages of the Gospel tradition, and often such progressive suppression or softening can be traced through the Gospels.
The evolution of the depiction of the Baptism of Jesus exhibits the criterion of embarrassment. In the Gospel of the Hebrews, Jesus is but a man (see Adoptionism) submitting to another man for the forgiveness of the "sin of ignorance" (a lesser sin but sin nonetheless). Matthew's description of the Baptism, adds John's statement to Jesus: "I should be baptized by you", attempting to do away with the embarrassment of John baptising Jesus, implying his seniority and the entrance of Jesus into his cult. Similarly it resolves the embarrassment of Jesus undergoing baptism "for the forgiveness of sin," the purpose of John's baptising in Mark, by omitting this phrase from John's proclamations. The Gospel of Luke says only that Jesus was baptized, without explicitly asserting that John performed the baptism. The Gospel of John goes further and simply omits the whole story of the Baptism. This might show a progression of the Evangelists attempting to explain away and then suppress a story that was seen as embarrassing to the early church.
Interesting what to make of it? Especially the last bit.