Here's my answer:
When comming out of the Oedipal stage of development boys believe that females have been castrated, and fear their fathers doing the same to them. castration in this sense is not physical mutliation, but oppresive social roles due to our genders. The boys eventually respect and identify with the father, repressing their desire to kill their fathers and have sex with their mothers.
The man you stabbed was doing something that is frowned upon in society - assault and theft. Since you associate with your father, and therefore authority, you murdered the man. But murder is also looked down upon - to uphold social order you must simultaneously rebel against it.
The difference between the cleanliness and dirtiness represent society as being "pure" and those who rebel as not. Ironically, whilst stabbing the man you had to get dirty to maintain purity.
Or, to make it short - you touch yourself at night.
"Beer is the mind killer. Beer is the little death that brings total obliteration. I will face my beer. I will permit it to pass over me and through me, and when it has gone past I will turn the inner eye to see its path. When the beer has gone there will be nothing. Only I will remain."
Make beer, not war.