Christmas Decoration

Snow everywhere, it's Christmas time. A person looks at the tree.

The person: "Only the last thing left to hang!"

He grabs a noose.

Explanation

Experiment

The joke plays on the double meaning of 'hang'. The person seems to be talking about hanging an ornament on the Christmas tree, but they are actually planning to hang themself with a noose. The humor comes from the dark twist and the unexpected turn of events.