It's a word, with a specific meaning. It was created to describe the sexist act of a man explaining something to a woman who either already knows, or is an expert in that field, as if she isn't smart enough to understand the subject. And frequently when a man is confidently wrong on the subject in question.

Without that sexist connotation, it's not "mansplaining." It's just being condescending. Like you.

So you're just an asshole? Unoriginal, try harder.