2 - 99% of the time it's what they have in their pants.

Sorry, but the idea that "the difference between men & women" is mostly "what they have in their pants" not only comes off as puerile, it's a completely male POV.

The most important of the sex organs insofar as being determinative of whether one is male or female are the gonads, which produce the female or male gametes (ova or sperm) and also produce most of the major sex hormones that each sex produces which gender ideologues are focused on, namely estrogen in females and testosterone in males. (Females physiology involves a lot of other sex hormones too, but genderists seem focused on estrogen as the female hormone that counts most of all.)

But the only people whose gonads are in their pants - or between the legs, to use the other phrase commonly used in these comparisons - are males. The gonads of female people are inside our abdomens.

There are thousands of physical differences between male and female human beings entirely apart from with "what they have in their pants." Like the size of the hearts and lungs; the differences in the cells and secretions of the respiratory tract; the shape, size and density of bones.

Also, it's not the norm in every culture for people to wear pants (trousers, breeches). There are a lot of places in the world even today where even males wear attire that doesn't involve pants.