Simpsons nerd here, this is kind of a late reply but I’d be happy to give you the context:
The “Say the line, Bart!” meme comes from an episode where Bart becomes famous after he says one of his catchphrases (“I didn’t do it!”) while guest starring on Krusty the Klown’s TV show. At first Bart is happy with being famous, but over time he grows weary of everyone always hounding him to get him to say the line. This leads up to the scene at the school where the entire class is staring eagerly at Bart, waiting for him to say it, to which he reluctantly complies after one of his friends asks him to say the line.
I think that all the time. As soon as they announce it, everone does exactly that 
