Years ago we had a horse that liked to bite. For him, it was definitely a game, and it had been inadvertently encouraged by his previous owner...playing slap and tickle. We got the horse for a song because of his biting habit.
It took a while, but we finally were sure we had broken his nasty habit. No hand feeding - period. No treats, no grabbing a handful of grass to give to him...nothing. When he tried to bite, it was full on war - a stout fist to the snout, yelling, screaming...made him move his feet, and keep moving them. It was almost funny to see the shocked look on his face the first time he tried it. And the second. And the third. After that, the nips became fewer and fewer.
Didn't have him very long - sold him to a young kid who wanted him for youth rodeo. Saw him every once in a while, but as far as I know, the horse wasn't biting any more.
Your horse's habit is not one that you can fix easily or quickly. However, it's a very dangerous habit. One you need to stop as soon as humanly possible before he bites the wrong person, which could land you and/or your parents in some serious hot water...
Plain Old Dee, horses Dancer and Rain I believe in dragons, unicorns, good men and other mythical creatures!