I used to be friends with a Nice Guy, but he didn't get super bad until we all went off to college. During high school, he was a typical nice guy and would just make stupid comments like "I would totally have a girlfriend by now, but all the girls I know are either ugly or taken." He was, and still is, a fat ass, and he dressed himself like an oversized kindergartener (sweatpants and those horizontally-striped shirts). He would never keep secrets, especially if he thought it meant he would get the girl. He also had anger issues and pummeled a friend one day because he jokingly kicked him in the butt. So there was that.
Once we were all freshmen in college, I ended up dating a guy from the old high school friend group. He was a rebound, and we ended up breaking up about two months into it once I realized the relationship was a rebound, and therefore not fair to him. Conveniently around the time I broke off the relationship, my cell phone number started getting signed up for all these bogus things. I got them taken care of, and things went quiet for a few months. Then one day, a random chick started chatting with me on formspring. We took the conversation over to AIM, and she started getting kinda weird. She would randomly bring up sex and talk about how much she liked anal, and if I had ever tried it. She'd ask me about my favorite sex positions, how many partners I had, and would then tell me all about her sexcapades. I soon realized she wasn't a real person, but I kept talking to her to see if I could figure out who she was IRL. I answered some of her questions in order to keep the conversations going, and it eventually came out that I had begun dating someone new. From there, she started sending me nudes and asking me to send her nudes. I kept telling her no, but she persisted. After a few more weeks of this, she gave up and stopped talking to me. I couldn't figure out who it was, and with time, I forgot about it.
One day about 4 years ago, my rebound ex got in touch with me. He started apologizing profusely, because apparently, Nice Guy tried to catfish me years ago in revenge for the breakup. He signed my number up for whatever services he could find, saved some nudes from a revenge porn website, created an entirely new AIM account to talk to me, and basically created this fake college-aged girl character in order to try to get nudes from me that he could post on revenge porn sites. Rebound ex found out, because one night he was hanging out with some of the high school guys, and Nice Guy got drunk and started bragging/ranting about it. Bragging, because he totally got "embarrassing" information about my sex life (he was the only virgin, so he's the only one who thought it was embarrassing or weird), and then ranting because the "stupid cunt wouldn't cough up her nudes". When one of the other guys asked why he would do that to an old friend, he said "to teach her a lesson after she broke (rebound ex's) heart." Rebound ex and I talked about it, I gave him my side of the story, and then we cleared the air in regards to the relationship so that we could end things on a good note. No one's spoken to Nice Guy since his drunken story, but I'm willing to bet he's not changed much.