The first episode where you change the channel if it comes on screen. The first episode where you don't just simply let it play through and ignore it, but actively fast forward through it to get immediately to the next episode.
In this episode Homer is exceptionally stupid and unlikeable, the scenario is so unrealistic that the suspension of disbelief required to even half enjoy it could induce a migraine, and the celebrity worship triggers a sense of second hand embarrassment so intense that I can't even look myself in the mirror after watching it in its entirety.
Before this there are many signs that the Simpsons is on its last legs, but this episode confirms without a doubt that the golden era has passed.