I thought it just represented him becoming a bit more positive in terms of his general outlook

Was the honeydew perhaps left in the background of the scene by a crew guy?

While it is a joke, its more about how self-righteous people will rant and rave about something they dislike, despite never trying it themselves. It is not a metaphor about change.

Yea man, the coffee cup was exactly what you said.

But honeydew is the moneymelon

The house is a metaphor for a home. Happiness is a metaphor for change. Everything is a metaphor. You are literally a metaphor!

the darkness is a metaphor for darkness

Just a nice little reassurance that people actually change

It’s not a metaphor but yes it shows that Bojack has changed he’s not the same person he used to be

yes

Despite always ranting about honeydew Bojack never ate some as far as we know - or at least not in a long time. When he finally tried it he noticed ist wasn’t as bad as he thought or remembered. In any case it shows his changes as he is willing to try something he thought he hates and accept the result. Old Bojack may have gone ‘well it isn’t thaaat bad but not as good as other stuff they probably just buy it because it is the cheapest option, even at a buffet in Hollywoo you can be sure to get proper food, why am I a star if they offer me the second best stuff blablabla’, grasping for any reason to turn his pleasant discovery into a bad expierence. But since he chamged he simply accepts it as the nice surprise it is, finally letting go of the negativity his upbringing drilled into him.

Both

Both, it was a recurring joke until they found an opportunity to make it a metaphor

It’s just a coffee cup. Or is it

i kind of take it as a sign of bojacks reluctance to improve. hes content sitting there and complaining about the honeydew instead of getting a better fruit cup, buying fruit and making a good fruit cup himself, buying something else that doesn’t have fruit in it, or even just not eating the honeydew. by comparison mr peanutbutter is also stuck in the mental age he got famous in like bojack but mr peanutbutter is able to enact change on the world where bojack wont change the world or himself when it would benefit him. mr peanutbutter would probably complain about the lack on honeydew and think of creating the change (fruit bowls without honeydew in them) before losing track of that project because he hasnt grown out of being a distractable young man

compare them both to someone like todd, who by the end of the show not only has realized his capacity to change (like mr peanutbutter has started to after dating pickles) but has also acted on his capacity to change himself and the world around him. todd would have no problem with just getting or making a better fruit cup, for himself or the world