They ride two abreast because the horse on the inside is inexperienced, they don't do it solely to annoy other road users. I used to ride and i hated going on the road because i always had nervous or unpredictable horses but because local councils have slowly got rid of bridleways (probably to save money) there are fewer and fewer places to ride so more riders are forced to take to the roads. A girl i knew lost a horse and a leg because of someones intolerant attitude and i'd hate to think that there are people with that kind of attitude on here.