To be entirely fair, my wording was terrible.
There's no real bad "reason" for a breakup, but one can have an ass idiotic justification and usually a poor justification is hiding some deeper personal hangup that the party is uncomfortable confronting.
A quick example: When I was nineteen, I was seeing a girl for about three months. Early on, she told me she loved me and I reciprocated. Our breakup occurred very suddenly to me and I had no idea what the fuck happened. We were hanging out at her cousin's house. She'd been drinking, I had not (I was straight edge at the time) and I conked her on the head lightly with a hair curler (NOT a curling iron, I'm talking one one of those little rubbery things you put in your hair overnight to curl it like you used to see on really old sitcoms) jokingly at one point and she flipped out and dumped me right there, in front of about four of five people. Her justification was that her last boyfriend beat her and what I did was textbook abusive behavior and she was clearly certain that I would inevitably become physically abusive.
Now, I was already a bit down due to various other crap already going wrong in my life and it was like four in the morning, so I couldn't exactly call anyone to vent, so I had to drive a little over an hour back to my dorm by myself in silence (My CD deck had been stolen that week) and, already being a depressive wreck, managed to put myself in the mindset that she must be right and I was a terrible person, so I drew inward for about a solid month. This actively fucked with me for a long time, to the point where I got to be nervous about even touching women for a time, much less having sex. I couldn't even get into a real relationship for about two years because I was afraid that if I got too emotionally entangled, I might become abusive or something. This got so bad that I started asking my mom if she'd ever dealt with anything from my dad, as I knew he did have a violent temper as a teenager (For the record, she said no and I believe her, as there has honestly never been even the most remote evidence of physical or emotional abuse in their relationship).
I didn't find out until 2006, almost three full years later, that she was actively full of shit. I actually got back into a relationship with this same girl, figuring we'd both changed and things could be okay. I'd finally moved past the complex I developed from the prior encounter and wanted to give it a shot. We got into a huge fight right before our final breakup where she admitted that she'd made up the entire ordeal because she was scared we were moving too fast and wanted out. Instead of telling me this forthright at the time, she instead chose to overreact to something in an effort to pin the blame on me and assuage her own guilt for getting in over her head in a relationship she was not ready for (Not at all coincidentally, our inevitable parting of ways was due to the exact same reasons, but I'd at least learned to recognize her pattern at this point and escaped with some minor binge drinking, some introspection and a slew of new relationship standards).
So yeah, all that to say: there are plenty of terrible justifications for a breakup. One should make sure they are honest about their justifications, though, because if you bullshit it in an effort to not look like an asshole, you may be doing a lot of harm, especially if you're dealing with someone who's already going through a gauntlet of emotional distress.
