Origin:

This meme started in 2008, however was based off of an episode of the popular children's cartoon, "Spongebob Squarepants" entitled, "The Secret Box", in which Spongebob tries to figure out what's in his friend Patrick's secret box. The scene of origin is in which Patrick tells Spongebob he can look inside, only to find that there is only a string. The meme is that when Spongebob opens the box, there will be something shocking or of comic relief inside replacing the original string.

Videos:

The first video known to start this was a video called "What's REALLY inside Patrick's secret box?" which was submitted on YouTube on June 29,2008. The video (which has disabled embedding), shows Spongebob opening the box, only to be met by a Rick Roll.

(The video can be found Here)

Soon after, dating about a year or so after, people started making their own videos of this.

Patrick's secret box revealed (Shoop Da Woop)

Dynamite

D**k in a box (PATRICK'S SECRET BOX FINALLY SHOWN ON TV!!!!)

Dickie (What's inside Patrick's box)

Patrick's box opens a portal from hell

WTF Boom