For me it was Lisa Goes Gaga. It was focused entirely on Lady Gaga who played herself and was awkwardly inserted, I don't mind the occasional brief celebrity appearance or when they lend their voice to other characters (ex. Meryl Streep playing Jessica Lovejoy in Bart's Girlfriend) but they started to feel so forced. I tried watching the occasional episode afterwards but people like JJ Abrams would show up in Do PizzaBots Dream of Electric Guitars? and I'd lose interest.
I have started watching the show again but I am curious who else has lost interest due to an episode or trend especially those who have been watching the show since its beginning.
The season 10 or 11 episode where the celebrities come to Springfield. Some of the laziest jokes in the series up until that point and it just fell flat for me. The whole bit with homer being too fat to parasail just made me roll my eyes.