horse (v.)youdaoicibaDictYouDict
Old English horsian "to provide with a horse or horses," from horse (n.). Related: Horsed; horsing. Sense of "to play excessive jokes on" is by 1893, mostly in formation horse around (1928), perhaps from horseplay.
[A] favorite pastime for many men is to "horse" or guy a friend who has shown himself susceptible to ridicule or fun making. "Horsing" is extremely wholesome mental discipline for over sensitive or super-conceited young men. "Horsing" always implies a joke at another's expense. As to how it came into use there is no satisfactory theory to offer. ["Yale Literary Magazine," December 1893]