I have to say, there was one particular biker near me that really had an issue with the horses on the trails. He would zip past every weekend I was out with my friends, and whip past missing the horses by mere inches(honestly - he bumped my boot twice). As he went by, he'd always say something nasty as well. As immature as it was, I got ticked off by him the last time he did it. There was a green rider with us, and he scared the crap out of her, and her horse. So, I decided to deal with it the same way he dealt with us - I ROARED up behind him, and whipped past him by inches with my big mare(she even switched her tail as we passed, so I know she smacked him in the face), then did a roll back a little ways past him so I could face him on the trail. He started in sputtering and starting to yell, and as soon as he stopped I very calmly said - it's no fun when someone roars past and acts like an ass, is it?
He's given right of way ever since. Def. not the way I should have handled it, but this guy was a real jackass. A big city guy with a 'cabin' out here in the country, that thought he had right of way, irregardless of the trail markings, and rules posted all up & down the trail.
Ask Often, Demand Nothing, and Reward Generously.