Well, for peeves, mine is eating. I can not stand a horse that eats, or tries to, while at work. Mine, the minute that halter goes on, food is off limits. I believe I developed this peeve as a little kid, battling with fat ponies over their next swiped bite. English people--do most of you let your horse eat while waiting around? I discovered this at a show last weekend that my gelding was ridden, and I had a talk with the little gal about not letting him do it (everyone--I mean everyone--else let it go). In western riding, it's kinda of a faux pas to let your horse eat--they are to stand quietly, even in belly-high grass, without snatching a bite.
That egg trick has a cruel cousin that I heard about from an old cowboy long ago; take a bottle filled with warm water, and when the horse rears, break it over his head. The eggs sound nicer, but on both, who the hell is going to cart those items along--particularly eggs--while waiting for the horse to rear?
I don't think anything mentioned here would be a total deal-breaker if I felt strongly about the horse; behavior can usually be modified. But, I do demand respect for my space and excellent ground manners--easily caught, puts head down for halter/bridle, stands back while feeding, leads on a loose rope a few feet away, good with feet, etc.