I agree with having a lawyer send a letter. And being me I'd post a copy of the letter on my bulletin board! No way the gossiper can "embellish" what the letter said!
I'd bet money that the horse that coliced, coliced from a obstruction. When a horse is starved they will eat anything to fill their belly - rocks, wood, tree bark, hair, just about anything. Then the horse's GI trac will coat the foreign object, much like a oyster making a pearl. Sooner or later that "pearl" will get caught somewhere. When that happens nothing can get past it, the horse colics.
I'm sorry the barn owner is having to deal with the crap! And you too! This kind of stuff is the reason I'm only in the barn early, early in the morning - when there isn't any humans around!
Tammie