Unforeseen Consequences- Short Story

Hi, I'm in year 10 and our next controlled assessment is based on creative writing. I have been assigned the task title 'unforeseen consequences' I have two hours to write a short story on anything that can fall under 'unforeseen consequences'. Has any body got any ideas for the plot?
Hope his makes sense
Thanks in advance for any help because I am hopeless at creative writing and your help will be muchly appreciated