Everybody at the assembled gathering begins to have an emotional reaction to the beautiful performance, resulting in enemies reconciling and people falling in love right there on the spot.
The film’s finale sees Will Ferrell singing “Por ti Volaré,” a love song, entirely in Spanish.
The magic of the moment is the punchline, though apparently for some the moment is quite real.
To be fair, the conclusion of Step Brothers isn’t a scene entirely without sentiment, it’s just that the sentiment is the joke.