A narcissistic womanizer finds the tables turned when a curse makes him irresistible to men. And the only cure may be consummating a gay marriage.

You could take a story like this many places. For me the first sentence worked fine as a logline by itself. Any more is only needed if you are trying to make a particular point ... and that risks narrowing the audience scope.

I thought it was pretty clear the curse is the inciting incident

It seems to me that for the premise to work it has to be the case that he suddenly becomes attractive to gay men AND concurrently repulses all women. He's lost his hetero-seductive mojo, he can't get laid. Women are rejecting him and gay men are hitting on him.

Thanks for your thoughts everyone!

The "cure" is an idea that the protag would consider when trying to figure out how to break the curse, among other things. It could be that it's not true and his sleeping with another man may be an extreme he goes to out of desperation. (Note sure if I want to do this, but it could be that *only* men are attracted to him during the curse. So if he ever wants to be with women again he's going to have to lift the curse)

But the general idea is that he only cares about having one night stands with women so the opposite of that (to teach him a lesson) is to be in a monogamous committed relationship with a man. Now how that would work or make sense is it's own issue. It could be that curse is lifted when he is *willing* to marry a guy but doesn't have to actually go through with it.

And it's a dark comedy so I don't mind being un-PC (as long as it's funny)

I believe the idea is that he chases women so he is cursed by being chased by men so he can see how it is from the other side. However it would be more poetic if being the victim of a one night stand was the cure.

I'll be honest - this logline did set off my PC-alarm bells. I'm sure it's not meant to. I think that perhaps including the sentence 'And the only cure may be consummating a gay marriage' is what it was. How is that the cure? In being a narcissistic womaniser, he is also a rampant homophobe?
Otherwise what is the point of the curse? Is the idea that he ends up confronting his dominant assumptions and challenging his prejudices?

How does he know what the cure is?

How about for the end of the logline "is horrified to find that the only cure is to consimate his marriage to another man".

Your logline needs an inciting incident. How about something like this:
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"After loving and leaving a young gypsy woman. a crass womanizer is cursed to be irresistible to men, and the cure... consummate a gay marriage."
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Hope that helped, good luck with this!