You might think that since someone has already written the melody, it would be easy to just match up your lyrics. That is not always the case. These videos did it best. Consider this a kind of Weird Al Award.
(Parody of "Boyfriend" by Justin Bieber)
Riley Wilhoit, Peyton Draper, and Kolos Urbanyi ft. Zora
(Parody of "______ In Paris" by Jay-Z and Kanye West)
Woo Jun An and Daniel Alvarez