He raped women!
There's nothing more to it than that. I mean during the campaign he was far more disgusting to the female candidates, insulting their looks and so on, than he was to anyone else but that just reminded people that a 70 year old dog doesn't learn new tricks. Do you seriously think no woman woke up on November 9th and felt less respected by society than the day before because of him winning? The whole point of trying to protest against him specifically rather than every little cause is that he made people who are liberals into angry liberals.
Same reason China, Mexico, etc all act dismissive towards him, he's a poisonous fucking mouthpiece that no one wants to give an inch to. The rest of the world was cheering Obama's win 6 months before he won (yaddda yadda bigger crowd in Germany than Bush ever got).