What is it to "hate [your] brother"?

I've just been working through a bible study in 1 John to be delivered next month (one likes to keep oneself ahead). I have spent considerable time looking at 1 John 2:9-11:

9 Whoever says he is in the light and hates his brother is still in darkness. 10 Whoever loves his brother abides in the light, and in him there is no cause for stumbling.11 But whoever hates his brother is in the darkness and walks in the darkness, and does not know where he is going, because the darkness has blinded his eyes.

It is a passage I have read many times before. The point John makes here is pretty obvious; if you hate your brother it seems highly unlikely you have been saved. If God is love (and light), as John says repeatedly in the letter, then those who abide in him are unlikely to exhibit lots of hatred (and darkness). A simple, yet profound, point.

What is almost never discussed is what hatred of one's brother actually looks like in practice. How do I know if I hate my brother? Is hatred and dislike the same thing? If I simply find someone annoying, or I get on better with someone else, am I written outside of God's love? If hatred of other believers is a mark of unbelief, how can I ever know the truth of the antipoint John is actually making, the assurance of my salvation, if this hatred is never defined?

I have heard some wildly contradictory (and, largely, unsatisfactory) views on what hatred of one's brothers looks like over the years. I am still not certain I could give any categorical definition. But, I offer the following as a potential starting point.

John spends much time outlining the differences between light and dark, love and hate, godliness and worldliness. These seem to be the fundamental contradistinctions John wants to make. Given this, it follows that hatred of one's brother can be identified by determining the defining features of love and inverting them. Though not exhaustive (1), Paul's list of loving attributes in 1 Corinthians 13:4-7 can help.

Paul comments on love:

Love is patient and kind; love does not envy or boast; it is not arrogant or rude. It does not insist on its own way; it is not irritable or resentful; it does not rejoice at wrongdoing, but rejoices with the truth. Love bears all things, believes all things, hopes all things, endures all things.

This might be inverted to read:

Hatred is impatient and unkind; hate envies and boasts; it is arrogant and rude. It does insist on its own way; it is irritable and resentful; it rejoices at wrongdoing, but not with the truth. Hate bears nothing, believes nothing, hopes for nothing, endures nothing.

Perhaps this is where we should start to assess our state before the Lord.

Notes

1. I do not think Paul is offering a definition of love here. I rather suspect he is outlining all the things the Corinthian church are doing and telling them that love would not do those things. It isn't a definition but rather draws some boundaries around what love is (or, is not)