The Triwizard Cup kind of represents the whole tournament itself: it could be a good thing that symbolizes and encourages "magical cooperation," but instead it turns out to be deadly.
What does that mean? Well, when Cedric and Harry are finally at the very end of the third and final task, and the Cup is in sight. Harry and Cedric, being good and honorable guys, do the whole "No, you take it…no, you take it!" dance until Harry concludes that they should both take it:
CEDRIC: Go on, take it. You saved me, take it!
Unfortunately, it turns out the Cup is actually a Portkey, and it takes them straight (do not pass go, do not collect $200) to Voldemort. Who then kills Cedric.
So, there you have it: both the tournament itself and the trophy that was its prize both turned out to be deadly, awful, and no good at all. But hey: it sure is shiny.