The art of snorting: Humans like to be snorted on. Everywhere. It is your duty, as the family horse to accommodate them.
Neighing: Because you are a horse, you are expected to neigh. So neigh - a lot. Your owners will be very happy to hear you protecting the barn and communicating with other horses. Especially late at night while they are sleeping safely in their beds. There is no more secure feeling for a human than to keep waking up in the middle of the night and hearing you, 'Neigh, neigh, neigh.'
Stomping cats: When standing in cross ties, make sure you never - quite - stomp on the barn cat's tail. It spoils all the fun.
Chewing: Make a contribution to the architectural industry - chew on your stall wall, the fence or any other wooden item.
Fresh bedding: It is perfectly permissible to urinate in the middle of your freshly bedded stall to let your humans know how much you appreciate their hard work.
Dining etiquette: Always pull all of your hay out of the hay rack, especially right after your stall has been cleaned, so you can mix the hay with your fresh bedding. This challenges your human, the next time they're cleaning your stall and we all know how humans love a challenge (that's what they said when they bought you as a two year old, right?).
Doors: Any door, even partially open, is always an invitation for you and your human to exercise. Bolt out of the door and trot around, just out of reach of your human, who will frantically run after and chase you. The longer it goes on, the more fun it is for all involved.
Going for trail rides: Rules of the road: When out for a trail ride with your owner, never go to the bathroom on your own lawn.
Holes: Rather than pawing and digging a BIG hole in the middle of the paddock or stall and upsetting your human, dig a lot of smaller holes all over so they won't notice. If you arrange a little pile of dirt on one side of each hole, maybe they'll think it's gophers. There are never enough holes in the ground. Strive daily to do your part to help correct this problem.
Ground Manners: Ground manners are very important to humans, break as much of the ground in and around the barn as possible. This lets the ground know who's boss and impresses your humans.
Nuzzling: Always take a BIG drink from your water trough immediately before nuzzling your humans. Be ready to rub your head on the area of your human that you just nuzzled to dry it off, too.
Playing: If you lose your footing while frolicking in the paddock, use one of the other horses to absorb your fall so you don't injure yourself. Then the other horse will get a visit from the mean ol' vet, not you.