When you start on one video then hit the link to a related video and then another related video until you've been on youtube for five hours when you started out looking at a panda sneezing and end up with some guy talking about reptilan aliens disrupting the human race's ultimate evolution to ascend to the 4th dimension.
"Hahahaha that baby panda is hilarious! Oooh, whats this video?" *four and a half hours later* "ZOMG! my mind is blown by how everyone in power is a shape-shifting reptilian! What a Youtube Safari!"