On Halloween, in the US, children go from door to door dressed in scary costumes. They say "trick or treat", if you accept treating you give them some candy, if you don't, they'll play a trick on you. But this trick-or-treater here is not a usual one, it's a dummy (a kind of manequin). This is what the authors of the video say:

"For our Halloween Prank we fixed up a life size dummy to look like a trick or treater complete with bag of candy and hidden microphone. Then we went door to door with our fake "Timmy" to see what kind of reactions we would get. We called it Trick or Treat With Timmy but it's been commonly referred to as the Fake Trick Or Treater Prank."

More pranks HERE.