To me, his opinion is just a mare's fart.
mare's fart
idiomSomething of no value, importance, or consequence whatsoever; a thing utterly not cared about.
Origin
disputed originFrom mare + s + fart. A nickname stemming from the unpleasant smell of the plant's leaves. Primarily used by cattle farmers in North Shropshire and Cheshire.
The politician promised change, but the voters realized his speech was just a mare's fart.
Despite the grand claims made by the marketing department, the final product proved to be a complete mare's fart.