Uploading... uploading... uploading... done.
When a file is uploading to a server, be it a web server or a file server, the user's computer immediately locks out and completely freezes, along with every single system on the local office network, making it impossible to work on anything else, in any capacity, while a file is uploading.
If it's uploading, you can't be working, can you? The 'perfect' excuse, of course.
If you often have to explain this perfectly valid reason to your superiors while you are browsing social networks in company time, you should get and wear this hoodie. This will make you much more efficient, having the luxury of not needing to explain yourself at all!