Sticking it to the man:
Performing an act of civil disobedience in order to oppose established power hierarchy.
Horses do it. Mules do it, too.
No, we’re not anthropomorphizing. We’re just using this slang term to help describe how horses lower in the herd rank can take advantage of a situation to give higher-ups a piece of their mind.
It happened during a recent outing with Pep and Jolene.
Thinking we all could benefit from some leg stretching, I rode Pep, ponied Jolene and took along Kip, the Ride-Along dog. We traveled onto Bureau of Land Management land in the Oquirrh foothills, walking and trotting through juniper and scrub oak. After a quick bite of grass in a small meadow, we hit a dirt road. It’s a rarity around here: wide and flat.
I asked Pep to move out. We were galloping, but there were hitches in her steps. Had she stumbled? Did a pebble get lodged in her hoof?
Without slowing, I looked around to check Jolene. The mule was taking intermittent Big Mac bites of Pep’s haunches. At a gallop. Without breaking 
her stride. Pep had been trying, without success, to kick out at Jolene.
In the pasture, Pep pushes around the bigger mule.
Jolene’s antics (which stopped when I yelled at her, but resumed when I wasn’t looking) seemed to offer little Miss Bossypants a certain comeuppance.