Have you ever needed to send a report or presentation, which was far from being complete, on a tight deadline? Have you ever needed to just "buy some more time"?
Here's a great solution. Take a file of the type you need to send (Doc, PDF, PPT etc.) and screw a bit with the bits, so it's no longer readable by its software. Send it to your boss/colleague/girlfriend on time, and do your best to sound surprised later when the other party claims the file is unusable.
Prepare a nice excuse, such as "It's my mail client", "my firewall hates zip files", "our spam filter does not allow Docs through" etc.
You can achive this result by using a simple Hex editor, or by renaming an already-corrupt file.
Or, if you are extremely lazy, you can use File Destructor. You can upload any file of any type to this site, and receive it back destroyed beyond use. Free of charge and no size limit.
Now, repeat after me: "the internet ate my file" .