Futurama has gone through two networks, over six seasons, and four movies, and while a lot of people have had their differences with its various incarnations, I, personally, had never seen a bad episode. Mediocre ones, yes, but not bad. "The Butterjunk Effect" was bad.
If you watched the Simpsons nine years ago, you've seen this episode done better. Remember back in season fourteen, when Marge got mugged, and channeled her fear into working out until she went on steroids and got scary-aggressive? Take out the funny and semi-poignant beginning of that episode, and pour on a bunch of bad humor, and you have this. The episode starts with Leela and Amy fighting. Leela and Amy have lots of differences. Amy is rich. Leela is poor. Amy is materialistic and spontaneous. Leela is ascetic and rigid. Amy has a PhD and a long history at the company. Leela dropped out of college and was only recently (in terms of the show) hired, and still outranks Amy. Although they've never really fought before, there's a great deal of potential. In this episode they make catty comments about sex and shoes, because someone saw the second Sex and the City movie and figured that's how women act.
They then deliver something to the moon, and watch a Butterfly Derby, where scantily clad women fly on butterfly wings and fight in teams until one team gets knocked out of the air. Amy and Leela team up and lose again and again, until they get sold Nectar, a "natural athletic supplement." After going on the juice they get verbally, physically, and eventually sexually aggressive, and also they refer to themselves as guys and the men as ladies, because that's funny. There's some twist at the end where Fry gets sprayed by butterfly pheromones, but not much comes of that. Leela and Amy resolve their passive-aggressive antagonism, which they didn't have before this episode anyway. And that's it. That's the episode.
The only good parts are the throwaway lines and sight gags that Futurama always excels at. A lunar hillbilly watching a derby says, when a girls wings are torn off, "You watch the floor, because that's where she's gonna hit . . . . Called it." The Nectar pusher, dressed as a gym coach, heads towards the door but instead sneaks away behind a bank of lockers. Other than that it's just a bizarrely weak and scattered episode which sets up a stupid conflict between Amy and Leela so it can be resolved stupidly.