I can recommend (speaking from personal experience) the following:

“Two Little Boys” by Rolf Harris

“Puff the Magic Dragon” by Peter Paul and Mary

“The Crazy Frog Dubstep Remix”

the ten hour mix of the Nyan Cat video

“I’m an Individual” by Mark Jackson

“Advance Australia Fair” (maybe even “O Canada” as well, for good measure)

and the Richard Cheese cover version of “Viva la Vida”

:)

For bonus points, serenade them with this: https://youtu.be/vDCziA6D4dY