This is a profound misuse of logic, a gross oversimplification, and a banner that allows people to behave in sexist ways while telling themselves that they're the victims.
Racism is complicated. When you look at a situation like Australia's invasion of the land it now claims, or Hitler's holocaust against the Jews, or America's treatment of People of Colour (now, definitely, but even more so in the past), we all agree: Negative attitudes from the oppressed towards the oppressor are more or less irrelevant compared to the un-justices being meted out against them. The power difference is so extreme that the 'reverse racism' seems... irrelevant. Breath, relax, we all agree. I am not about to attempt to tell you how, as a white Australian, I am as oppressed as the original occupants of this land.
But racism is not anywhere near that clear-cut, most of the time. Take the Isreal / Palestine conflict; or the simmering racism between various Asian nation-states, like South Korea and Japan. Or even the USA / Russia conflict as it stood in the early eighties, when both sides were more evenly matched (and threatened).
It's complicated. It's nuanced. Both sides are entitled to claim victim-hood. There is no clear winner or loser, and both sides commonly feel like they're more hard done by.
Sexism - at least in Western modernity - is not as simple as a holocaust, invasion, or annihilation. The gender war is complex and nuanced.
Men win in the areas - to generalise - of politics, business, employment, economics, and sometimes physical strength. Women win - to generalise - in the areas of family, friendships, community, communication skills, emotional fluidity, and sometimes physical appeal.
Men may get paid more, but are more likely to die or be injured on the job. Women carry the emotional load, but are overall happier. Men will die younger, but richer (neither for any good reason). Women are freer to speak in community settings, but less free in business settings. Men are more likely to commit crimes, but get 150% of the sentence women get for the same crime. These comparisons go on forever.
It's complicated. It's nuanced. Individuals within the gender war will sometimes be in positions of privilege, and sometimes disadvantage; gender will sometimes play in their advantage, and sometimes not.
To say that sexism never happens to men is to say that racism never happens to Israelites. Or Palestinians. (Depending on what side you're listening to). It is to say ageism never happens against young people. (Or old people). Or that nepotism never happens to [group x]... you get the picture.
Personally, I have come to dislike the racism-sexism argument because it's generally followed by something really sexist, against me. The speaker will feel completely justified, because as far as they're concerned, they're off the hook. They're not the problem. They're the victim. If anything, they're just evening out the score, and that's justified.
That's what everyone fighting a war has told themselves, regardless of whether it's an evenly matched or hopelessly one-sided war. It doesn't mean they're right; it may just mean they're one-sided.
Yet at the same time, I am patently aware that what new Australia has done to indigenous Australians is wrong, wrong, wrong, and continues to this day. Any racism directed towards me (as a white person) is irrelevant.
Confusing? No, not really, just complicated. Please stop talking like it's simple. Racism and sexism are not the same, and sexism is not something that only happens to women.