What does "Fat fish in a sand"? mean?
Hello.
Could someone clarify that please?

Mr. Pig: Haha... all right, sweetie. Thank you. [they both kiss, goes to pull lamp cord] You're gonna come with me to Princess Bubblegum's firework show tomorrow?
Tree Trunks: No, she whizzed on our wedding. I'm sorry, but she's a fat fish in the sand.
Mr. Pig: I want to see free fireworks, though, and I want you to come with me.

Thanks

Question

What does "Fat fish in a sand"? mean?
Hello.
Could someone clarify that please?

Mr. Pig: Haha... all right, sweetie. Thank you. [they both kiss, goes to pull lamp cord] You're gonna come with me to Princess Bubblegum's firework show tomorrow?
    Tree Trunks: No, she whizzed on our wedding. I'm sorry, but she's a fat fish in the sand.
    Mr. Pig: I want to see free fireworks, though, and I want you to come with me.

Thanks

Answer

I've never heard this before but i know
When a fish is out of water and on the sand it trys to flop back to the water but a fat fish would have problems doing that.

So i think it means something or someone who is in the way (annoying) and is useless.

Or something like that.
I don't really understand it myself but i hope that helped some

Answer

Thanks, Kat!)) Yeah, they made up lots of phrases. But I can catch up some slang phrases so far))
Thanks anyway =)

Answer

Adventure Time is a cute show, but it uses a lot of made-up phrases that don't actually exist even in English slang. If you are using television to help with learning English, this show would not be my first choice, although there's no harm in watching it for entertainment and general exposure to the language.