This is really not such a silly question PC. We usually associate the word 'enemy' with something not pleasurable and therefore we tend to dismiss the thought right out of our minds without looking at what the enemy can teach us about ourselves spiritually.
Essentially, the 'enemy' is the embodiment of everything we find disagreeable. The 'enemy' is the personification of our own bias, prejudice, our fears, the opposite of our willful opinions, the crack in our self righteousness and the thorn in our comfort balloon. Having the enemy gives us the opportunity to ask what it is that made the person our enemy. It is a chance not to focus on the enemy's actions but our reaction towards the enemy's actions.
For example, if the enemy slandered us and we feel deeply aggrieved, it is an opportunity to examine if we are very attached to a certain kind of reputation that we would prefer to have. When we closely examine it, the reason I am aggrieved is not really the enemy's slander...there are after all, empty words, but my own hurt feelings as a result of being denied my strong attachment to having a good reputation. And we become unhappy because we always associate happiness with our attachments. Fundamentally it is our attachments. A 'Friend' is our attachment to Happiness and things we Like and an 'Enemy' is our attachment to Anger.
Although it is a lot easier said than done, an enemy is the beginning of the training to combat the Eight Worldly concerns. And if we are serious about our own spiritual growth, then the enemy becomes not the object of our practice but the trigger to remind ourselves of that practice.
As we all know, the true enemy is a mind that shouts: I want, I like this and don't like this, this ticks me off whilst this other thing makes me happy, I want more, why can't I have more and so on.
In this sense, this enemy should be considered one's best friend! Best friend are the ones who tells you the truth about yourself. Otherwise, all the friends we have are fake friends who wants to maintain a good relationship for some benefits or have some hidden agenda. How can we be faultless and perfect? Impossible.
Hence, we should keep an open mind, realise that we have faults, be grateful when someone is so kind to point out our mistakes. Do you think it's easy to do so? Many times, people dread telling people off cos nobody want to see others negative reaction from it. It can get quite ugly and pleasant. It is very tiring.
At the end of the day the real enemy is really ourselves.
Why someone would like or dislike us does not depend on the other person, it is because of us. Sometimes you really cannot help it, like if a person is jealous with what you have as mentioned, but sometimes it may be because we offended the other person by something we said or did, and we didn't realise. In all cases, yes, maybe you did no wrong, and just be who you are sincerely like what PC said about his teacher who only tells the truth, but there are still people who doesn't fancy you.. Don't think you can do much about it. Just don't retaliate, don't harbour anger back towards your "enemy".. the best you can do is just to be sincere with them, and continue on doing your own thing. I find the 8 verses of thought transformation helps with this. There's always two sides to something... in the end, they'll all come around if they feel your sincerity. Otherwise, leave it as be.
Well, I believe that it is more important to know what to do with our enemy than about having enemies. Real outer enemies are kept at bay when we are kind and do not retaliate their harm with more harm. If we are attained, we can even return kindness with the harm we have received. That's a true Bodhisattva-like nature. If we are not at that level, at the very least, we can strive to work harder to prove our enemies and naysayers wrong. Our enemies can make us stronger and more motivated at our spiritual practice and Dharma work.
As for inner enemies, we have to suppress them and ensure we are not them and they are not us. Our inner enemies like anger, impatience, laziness and so forth do not define us and we should not identify with them and instead find ways to alienate these qualities within our minds so we can easily minimize these qualities and eventually get rid of them once and for all. Lots of practice, studies and reflection is needed to get rid of the toucher more subtler inner enemies like ignorance. However, it is better that we get rid of them or we become what others identify us with.