What is an Enemy?
A proper definition of 'enemy' generally contains terms such as 'opposition', 'hostility', and 'hate' and implies that the other party is aware of these feelings. While we can conceive of unfounded, delusional hostility toward an individual, the formation of an enemy is typically fueled by neglect of duty, gross misunderstandings, consistent disregard for personal well-being, and the like. Experience also leads us to conclude that these feelings are frequently reciprocated, though we cannot assume that they follow out of necessity.
An Enemy is NOT...
Implicit in the definition of 'enemy' is the existence of another living, and generally rational, being. While we may be in direct opposition to ants and consider them as an enemy, for example, it would not be entirely consistent with the above definition upon which I base this discussion. To further limit the word 'enemy', we need look no further than disbelief. Atheists, though often in opposition to the organization of religion and the dutiful worship of glorified imaginations, are not opposing some real, verified truth but rather the obvious contradictions and disturbing hatred littering the pages of supposed infallible texts. It is no more correct to call the atheist an enemy of 'God' than it would be for us to consider someone to be an enemy of the tooth fairy. While a person, namely an adult, may exist who believes the tooth fairy to be real, the rest of the world would not be correctly categorized as enemies on the basis of their disbelief.
Becoming an Enemy
Having established all of this, I must say that disbelief does not remove any anger directed toward the Christian god when I hear family members expressing their concerns that my children will be going to hell if I neglect my priestly duty (as priest of my house). Were god to exist, particularly the Christian variety, I an not sure that 'enemy' would be the correct term. What do we call someone who demands life-long servitude on the guarantee that the wrath of hell will only be poured upon the insolent and unbelieving? Do we call a torturing, hide-and-seek, jealous, unforgiving being 'Wonderful' or an 'Everlasting Father'? Only if we are confused about the meaning of such terms.
Paul suggests in Philippians 3:17-19 that those who are not following his version of the story are "the enemies of the cross of Christ". The writer of Hebrews states that those who willfully sin after receiving knowledge of the truth (that Jesus died for their sins and demands repentance) have the judgment and fiery indignation of God awaiting them. In what God considers an act of war, these sinners trample upon the Son of God, regard the blood of the covenant as unholy, and have insulted (done despite unto) the Spirit of grace. "This attitude reflects a repudiation of the validity of Jesus’ death as a sacrifice for sin, and throws back in his face every blessing flowing from his loving heart. It is difficult to imagine the hardness that is harbored in the soul of one who is so incredibly insensitive to divine love." (Jackson, 2005)
How angry can this good god be that we don't believe? Of course the world is insensitive to divine love; all that can be known of God is evident in a world which generally tends toward chaos. There certainly are a few neat things in the world, but these exist next to the most disturbing physical, mental, emotional, and sexual abuses. We see from the suffering of hungry children and people with severe disabilities that god's eternal and infinitely good plan included all of this. The unconvinced need look no further than the biblical passages wherein God promises to answer when we call to him.
Examine the following graphic provided by RAINN:

These values do not include victims under the age of 12. It should be safe to say that at some time within a week, someone is abusing a child below the age of 12. Imagining for a moment that somewhere in this world is an innocent Christian child who is being physically and sexually abused. She has cried out for help from her parents, but they are not near. Sunday school stories of Gentle Jesus come to her mind. The words of that old hymn rise in her head as she wishes her assailant would leave her.
"Gentle Jesus, meek and mild,
Look upon a little child;
Pity my simplicity,
Suffer me to come to Thee.
Fain I would to Thee be brought,
Dearest God, forbid it not;
Give me, dearest God, a place
In the Kingdom of Thy grace.
Put Thy hands upon my head,
Let me in Thine arms be stayed,
Let me lean upon Thy breast,
Lull me, lull me, Lord to rest.
Hold me fast in Thine embrace,
Let me see Thy smiling face,
Give me, Lord, Thy blessings give,
Pray for me, and I shall live."
Perhaps at this point, you have already imagined the fear and torment surrounding this imaginary, though often true, situation. Were these things to happen on my watch, were I to meet you in a coffee shop or restaurant and inform you of a child that I saw in an alley experiencing such atrocities, you would be indignant were you to discover that I just left her unassisted. "I have mysterious ways beyond your comprehension," I'd say. Would you suffer me to live? Would anger compel you to action? I should hope so, but then again, we are just evil people well below God's magnificent standard of living. It is for this reason, the obvious lack of guidance, that we are told to be imitators of God. Could you force yourself to imitate God in this situation? What about starving children who nightly go to bed, their stomachs crying to God for a crumb from his table.
Conclusion
Steven Weinberg said, "God in the Old Testament tells us to bash the heads of infidels and demands of us that we be willing to sacrifice our children's lives at His orders, and the God of traditional Christianity and Islam damns us for eternity if we do not worship him in the right manner. Is this a nice way to behave? I know, I know, we are not supposed to judge God according to human standards, but you see the problem here: If we are not yet convinced of His existence, and are looking for signs of His benevolence, then what other standards can we use?" In reality, we cannot be an enemy of something of which we are not convinced to be true. This, as I stated before, does not prohibit us from being enraged at fictional characters; I shall continue to consider myself an enemy of the idea of Christian god.
References
Jackson, W. (2005, July 21). The Crimson Flow. Retrieved May 6, 2008, from http://www.christiancourier.com/articles/read/the_crimson_flow.