A total nightmare, hassle, or situation that’s gone proper pear-shaped. You’ll hear it as What a mare or It’s a mare when your day turns into a string of small disasters, from missed trains to tech that won’t work. Not about horses, just misery with a bit of British understatement. Honestly, a lifesaver of a word.
"Got to the station, train’s cancelled, phone’s on 1%, and the lad in front’s eating egg mayo like it’s perfume. Absolute mare, I’m off to the chippy"