"irritating, offensive, extremely annoying," 1580s, figurative use of present participle of gall (v.).
"to make sore by chafing," mid-15c., from gall (n.2). Earlier "to have sores, be sore" (early 14c.). Figurative sense of "harass, vex, irritate, chafe the spirit of," is from 1570s. A past-participle adjective gealled is found in Old English, but OED says this is from the noun. Related: Galled; galling.