I have had a couple of situations like that - in fact, I have had too many places where neophyte directors/designers/etc assumed I didn't know my ass from a hole in the ground just cuz I was female - so truly, I feel your pain. Here are a few things that worked (sometimes), depending on how obnoxious this person is being (does he ignore you or brush you off or say things or...?)
You need to put on your tech-week patience and good humor hat, and be as manipulative as you would be w a recalcitrant actor who needs to be ready to go on.
again, this is just a handful of things I've done that were successful, but it oughta get you started
- mention to said designer that a specific actor or actress (esp one he likes) really needs to understand how something on the set works, and you don't want to waste his precious and important time so if you can get the groundplan so you can tape it out, it will help that cast and/or crew member (and once in a blue moon, if it's someone you trust and who knows/sees the situation, you can bring that person into the mix so they can help you)
- ask for advice from him. Really. Sexist jerks can't resist teaching (even if it's something you already know) cuz it's a chance to show off how much they do, or don't, know. Now, don't ask something stupid, but maybe there is a gag that is a tad challenging, or a set piece that requires a little visual to make work, and you can ask abt it, relating it to a specific moment in the show - you can also ask advice/help for something NOT play-related in which you both share an interest, like, I love that you worked at such-and-such a theater or on that/this show - tell me abt your experience, I want to work there/ do this and would love your input
- go thru the other designers - costumes, lights, props etc all need to know what the set looks like (and colors and etc need to be coordinated) so letting them lead, esp if they know this person's rep, will not damage yours.
- thank that person honestly but profusely when he does things that help you do your job. Show appreciation for even normally taken-for-granted help (like say, providing a groundplan).
- find something you both have in common (from other folks, of course) - that ALWAYS helps and removes you from "one more female SM who couldn't possibly know what she's doing" to "fellow kung-fu afficionado" or whatever
- chat w the director/producer and explain your problem, not from the perspective of getting the guy in trouble but explaining that you need your tools to do your work. Make sure they know, without blame or emotion, that you are trying to get your job done in a civil, polite, professional way.
<on edit> - oh yeah - never, EVER play the girl card - without saying anything, just be ready to work harder than any of the men, and don't let him assume (or, for that matter, know) you are on the rag at any moment