How do you answer 'Why did you leave your last job' in a job interview if you were fed up with the reprimands and just walked out?

The best way is to give a positive answer... rather than focus on the negative aspects of the job, talk about what you did enjoy and how those things relate to the position you are aiming for. Then explain that you didn't feel comfortable in the workplace and felt you would be able to bring out the best in yourself elsewhere. It would perhaps be a good idea to say "It's important that you enjoy your work and I look forward to (or the possibility of) a fulfilling career(permanent)/job(part-time-temp) with yourselves"

- Use Wording that you feel is appropriate and you comfortable with - All questions in an interview should be answered in a positive manner, even negative questions like the above can be used to your advantage and don't forget you are there to sell yourself!