This terms are based in the --false-- claim that [all] men are dominant and [all] women are passive and unable to defend themselves from the big-bad-male. They aim for a society uniform when people will have much less margin to be an individual, and people with long legs or that weight different will be ashamed for that. Both terms, mansplaining and manspreading evoke a very dystopian feeling.

But if this is the kind of society that you wish for, feel free to spread the sticky mess

Mansplaining is the phenomenon of which an arrogant male-persons arrogance can be attributed to their sex/gender (as appropriate), usually with some reference to "patriarchy" and the undeserved confidence of those higher up in the power hierarchy when belittling or underestimating those lower on that same scale.

In practice, it is a gender-specific, weaponised term used in any situation where a man is perceived to be arrogant towards a women i.e. it is commonly abused beyond any positive philosophical aims.

Maybe it has a similar reasoning i.e. men sexist-ly assume women know less than them - but the fact is that it is rarely clear b/c arrogant, narcissistic people of both genders exist without the need for such a basis.