Gall describes something irritating, like someone very rude. If you barge into a bakery and cut in front of a sweet old lady, then you have gall.
If someone has gall, they're irritating. In fact, as a verb, gall means "to irritate" like new tight jeans that gall your thighs. Gall is "bile," too, like what's in a gall bladder. Back in the days of Hippocrates, if the four humors of the body were out of whack, it affected your spirits. If you had too much bile, or gall, then you'd be aggressive or depressed. It's also a noun for "deep feeling of ill will."