Credit:
In this particular case, a couple of Domino's employees have filmed themselves doing gross things to food that'll probably get served to customers, and posted it to YouTube. Due to reactions and some quite clever investigative work of appalled viewers, both were promptly fired.
For the rest of us, it sadly shows that these things (hopefully, very rarely) do happen in restaurants. It also shows that, luckily, people who are dumb enough to do something like that are also incapable of understanding that posting something on YouTube means that the entire world can see it. Kudos to that.
If you're not easily grossed out, the offending video is below.