You might have a bad product owner and fail at scrum if your product owner:
- interrupts sprints with side projects.
- diminishes the impediments you bring up and/or claims they're just 'the way things are'
- watches and allows team members to be abusive to eachother or not adhere to scrum values.
- hides the true velocity from the executive sponsor
- doesn't bring stakeholders to the table for planning and/or keeps them at arms length from the developers
- decides things for the team on specific implementation/doesn't empower the team to make decisions
- leads by politics instead of business value
- is passive aggressive
- doesn't take responsibility for the results of a sprint
- doesn't participate in sprint planning
- doesn't prioritize effectively/constantly
- doesn't keep the backlog estimated by soliciting estimates from team
Remember, product owners are people too... sometimes they just don't understand agile/lean practices and are simply too use to traditional methods.