When the horse is...
Resistant to being caught
Constantly pulling when led
Pulls back or gets stressed when tied
Swishes his tail every time you walk behind him
Always is moving away when trying to tack him up
Steps away when trying to mount
Walks off as soon as the rider is in the saddle
Is drifting, bracing, or anticipative when ridden
Takes "a while" to load into the trailer
Might explode backward during the trailer unloading
Is "buddy" or barn "sour"
Has the same "issue" with the same scary spot repeatedly
Offers dramatic behaviors when something unexpected arises
Paws, paces, cribs, weaves, wall kicks, bites while in his enclosure
Is aggressive towards other horses or at feed time
Etc., etc., etc.