I'm not certain it's so much that there's a double standard as a general feeling of powerlessness that's not being expressed very well. Gay people can certainly be (and have been) jackhats to straight people. The consequences of it aren't quite as compelling, though. Prop 8 is a good example. Bunch of frightened straight people got together and decided to deny something to a minority group because they didn't understand\were being vindictive\believed propaganda.
LGBT can't do something like that. As individuals we can be jackhats to one another, but there are definitely differences in the way that jackhatishness can manifest and it's historically been in favor of the majority. So, there's a perception there that the harm isn't quite on the same level as the people who have real power to take things away from that smaller group.
No, it's a double standard, especially when people b**ch and complain about it in this day and age when it's illegal in civilized nations to discriminate against gay/black/[insert minority] people. Just because of group of retards who are too stupid to tie their own shoes pass some kind of legislation (not even federal legislation) doesn't make it okay (or, at least, not as bad) to be an a**hole to straight people.
Also, lolwat? LGBT most certainly CAN do something like that. Since the media is so up-in-arms about being politically correct, all it takes is for someone who isn't in a minority group to say something that could be misconstrued as homophobic (even if the intent is very clearly not) and LGBT activists will jump on it and use it to demonize the person who said it and turn that person into a pariah.
Again, the whole notion of "well, there are more straight people than gay people, so gay people can't really be discriminant towards straight people" is f**king stupid. "I'm allowed to be a piece of garbage to them, there's more of them than there are of me!" is illogical and mean-spirited. People who advocate that don't want equality, they want advantages and special treatment becuase they happened to be born a certain way. That's just another form of elitism. "Oh, you're not gay? Well, f**k you, you don't get pandered to by anybody, and you don't get to complain, you're STRAIGHT."