It's not fair that my boyfriend can say "I'm good" when he's not in the mood and I make sexual advances, but that when the tables are turned, I'm expected to give him what he wants, amirite?

You could always say, "actually, you're not good, so I'm going to sleep now! Let's talk about this in the morning."

It depends on the case. If it's like he wants some every couple of days, but you only want it every couple of weeks, you shoot him down a lot more than he does you. On the other hand, the rarity of your mood would make it somewhat a commodity that he would jump at the opportunity to get, but back to the first hand, should somethign like sex really become a commodity?

In another case, when both are equal, this is bullshit. Neither of you should have to do anything you don't want to do.

Then again, if you're only in the mood even less frequently, like once a month or less, it is rather unfair to him to have to wait that long, and you should at least let him try to put you in the mood.

All these can be reversed, but from your scenario, I get the feeling that he wants it more often than you.

Ya that's total horse shit, it goes the other way. When a guy asks a girl if they could have sex and she turns him down guys are expected to think 'ya I guess this happens from time to time no big deal' but if a girl wants to have sex and the guy turns her down for some reason society thinks she has the right to get mad at him and sad that he 'doesn't find her attractive' as if the only moods guys have are 'horny' and 'no longer attracted to you' it's a crap standard.