A
4chan meme which started on /v/. Since /v/ is ostensibly a
work-safe board, people assume it's completely safe to browse the board at
work (hence the name). One day, someone posted a
NSFW image, and one person posted "My boss walked by when I had the image open at work, and I got fired." Someone responded "I got promoted," implying he was promoted to replace the first guy. Soon after, when someone posted another work-unsafe image, one person responded "PROMOTIONS!"
People unfamiliar with the phrase's origins believed it to be wholly ironic, and thought it was so hilarious they repeated it whenever work-unsafe material finds its way onto the board, and then it became a true
meme.
It should NOT be assumed that bosses like to see their workers watch porn at work.