Well, imagine this (and I know this is not a totally realistic scenario, it just conveys a point). If a masochist follows the golden rule, does that masochist become a sadist? It seems to make sense. They want pain done unto them, so do pain unto others.
But, we can assume that a good portion of the population isn't masochistic in this manner, and would object severely to having pain bestowed upon them. This an example of where different values cause a serious problem for the golden. The world would certainly be a worse place for at least one party in this scenario.
I don't think that the Golden Rule necessarily applies in EVERY situation for EVERY minutia of human interaction, but nobody is saying it need to either. It's called "Golden" because of it's perceived value or relevance in human interactions, not some Midas reference
With that said, I don't think that the masochist example is a fair one. For one, I wouldn't say the Golden Rule applies to self destructive behavior. In fact, just being a sadist probably violates the golden rule. But I think the masochist description is a little misleading. Even if you accept that it is not a destructive behavior, a masochist doesn't want just pain, they want pleasure - they just happen to derive that from pain in some circumstances. I doubt a masochist would WANT to be walking down the street and then have a gang jump them and beat them half to death, but throw them in someones dungeon bedroom with a wall of whips and their happy. If you could apply the golden rule to this situation (and this is probably not realistic either), a masochist would only 'perform' with a willing partner (otherwise forcing it is a violation of the rule), and would have to be willing to inflict their 'pain for pleasure' on the willing partner if desired. And even if they did 'inflict the pain', it wouldnt necessarily make them a sadist, as they might not derive pleasure from that action.
If a person objected to pain being bestowed on them, then the masochist/sadist wouldnt inflict it if they were following the golden rule. The masochist may want his pain, but they will never get it from an unwilling counterpart, and the rule doesn't indicate he necessarily should. But if a mashochist does apply the rule, he is probably more likely to find a counterpart willing to give him what he wants.
The rule never states that if a person does x, he will get x. Whether or not a person gets what he wants is irrelevant. The rule is proactive, not reactive. A person will act on principle, regardless whether it is returned or not. Most people want respect and kindness. The rule is there to foster such. Someone practicing respect and kindness may not get it back from everyone, but nothing in the rule said they would. But I bet that someone practicing respect and kindness towards others will more likely than not do get it back from some, probably others applying the same rule. And if everyone did that, the world would be a better place.