A friend recently used the phrase 'bane of my existence' and, while I'm familiar with the phrase, I would like to know its origin and meaning.
bane: a cause of great distress or annoyance
Therefore the bane of your existence is the chief annoyance or distress in your life, it is something that prevents you from enjoying life, turning it instead to misery.
From White Fang by Jack London:
Bane itself is an unusual word in English and outside of this common phrase it is rarely used in the modern language. According to phrases.org.uk it was present in the Old English Chronicles and meant 'murderer'. It can also be found in the common names of the plants henbane and wolfsbane, both of which contain deadly poisons.
"Bane" is a somewhat archaic word implying that the thing being described is good for killing (or at least getting rid of) something else. For example, wolfsbane is a plant that was traditionally used to poison wolves.