uk.misc had a years-long habit of shouting "HORSE" after someone turned up trying to trace some Canadians who "moved to Burton-on-Trent and stole my HORSE".
uk.music.folk would shout "HORSE" too, but for a different reason: whenever the old "ah but is this really folk music" argument was trotted out. It was a reference to Louis Armstrong's "all music is folk music - I ain't never heard no horse sing" (https://www.smithsonianmag.com/arts-culture/all-music-is-fol...).
And back in the early days of OpenStreetMap we had a running gag about horse=yes, after early finding-our-way attempts at the tagging folksonomy resulted in 70mph highways in Britain being tagged with "horse=yes" because, yes, legally you were allowed to ride a horse on them.