Actually you can report them, but must do so carefully. If someone has a Friendly Honor Ribbon, and are decidedly unfriendly as a matter of course, then their honor is suspect, and could be the result of honor trading, which is reportable (as spamming). Same thing goes for Teamwork and Honorable Opponent, and even Helpful.
However, lack of the recognized attribute should not be construed as its absence. If someone has a red ribbon and doesn't "GG" at the end, you shouldn't report them for that; not every honorable player is 100% consistent. But if they have a red ribbon and they end with "ez game nubs", that's clearly not in line with being an Honorable Opponent, and you might consider reporting them for honor trading. Also note that deficiency in one type of honor does not negate the veracity of another type. For example a player could excel at Teamwork and still be unfriendly, so only consider this if they're displaying qualities that directly contrast their award.
Honor may not have readily tangible benefits right now, though Reds have hinted at the possibility of future tangible rewards, but that doesn't mean it's meaningless or totally subjective. It at least shows a certain respectability which should niether be taken lightly, nor falsely traded.