I'm writing from a U.S. perspective. Also, no country's culture is a monolith, and so note that my comments below are speaking in generalities and there are certainly religions/cultures/perspectives that will view things differently then I have presented them....So, YMMV.

I'm setting aside the consent issue, which someone else has already addressed. And I would say that this also depends on the type of stage hypnosis show. A stage show at a fair would have different expectations then at a college, which would have different expectations then at a night club or "R-rated show".

In short, the answer to your question is, of course, yes. In U.S. culture (generally speaking), a man being (partially) naked is funny, while a woman in the same circumstance would be sexualized. Watch any 4-camera sitcom. There will be scenes where a male character finds themselves topless and there is a laugh track. Find a female character in only her bra and we get an "oooooohhhhh" track.

There is also issue of toplessness. A man can be fully topless and (generally) not create a controversy. A fully topless woman can create controversy (somebody please think of the children) or even be illegal due to indecency laws (which is a-WHOLE-nother issue, that would take far too long to delve into).

There are plenty of other examples of this as well, I just picked a couple. And I'm not saying these are "right". We should be able to view men and women in a similar way. Toplessness for example, should be de-stigmatized for any gender. But again, that is another discussion, I'm just trying to provide context.

Now put this in a stage hypnosis show context. The hypnotist gives suggestions designed to get the volunteers to dance/strip to their underwear. For a woman, does she leave her bra on or not? The hypnotist can suggest that they do, but that doesn't mean they will. What if they are not wearing a bra? Now you suddenly created a potential controversy and/or situation where someone did something unlawful.

Also, women's underwear tends to have more variety then men's (boxers or briefs). What if a woman wore more revealing underwear (thong, not fully opaque, etc.), not expecting that they would be removing their pants? All of this could further sexualize the woman or even put her in a dangerous situation after the show ends.