Coersion. For example, “if you don’t have sex with me right now, we’re breaking up/I’m divorcing you/I’m going to ruin your life by doing xyz.” And when you say no, she’ll threaten to call the cops on you for some made up bullshit, but they’ll believe her over you because she’s the woman and you’re the man.

Also, you don’t have to be erect to have someone force you into performing sex acts. She could force you to perform oral on her, she could grope you, she could even penetrate you.

But if this happens to you, fight back.