I was only a girl for a while so I didn't get to experience much of this. The only time I had to turn down a guy in high school he: cyberstalked me, sent me tons of anonymous messages, made many alt accounts to lurk in my friends' group chats, impersonated me to break up with my then girlfriend on a day he knew I wouldn't be at my computer, sent me sexual/threatening messages for years, then told lies about me when I tried to tell adults. Because he was a lonely kid and I made the mistake of being friendly with him at school.
So yeah I they can be freaks when you don't give them what they want