It’s time to solve a mystery of your noodle arms,
(Dipper is wondering why Finn has noodle arms. To note: something humans don't have. This is pretty ironic, considering that Dipper also has noodle arms.)
Are you trying to get your own brother harmed?
(Jake is Finn's best friend, although he considers him as a brother. Sometimes he gets Jake in danger or hurts him.)
Your hat looks like a bunny who’s really dumb,
(Dipper is comparing Finn's hat with a pair of bunny ears. He's also saying that Finn is an idiot.)
My sister made a sweater for you, made out of Princess Bubblegum.
(Mabel Pines is Dipper's twin sister. She likes to make sweaters, wearing a different one every episode., something cartoons don't usually go by. Dipper is implying that Mabel made a sweater off of Princess Bubblegum's hair.)
Adventure Time? it’s already noon,
("Adventure Time" is Finn's catchprase and the name of the show itself. The joke here is that it's not the time for adventure yet.)
If anyone in the Land of Ooo is a joke, it’s probably you.
(The Land of Ooo is where Finn, Jake and Finn's other friends live. Dipper is implying that Finn is silly.)
This is Gravity Falls, guess what? you fell,
(A bit of word play on the title of the show Dipper is from, Gravity Falls. By saying Finn fell, he means that he already lost the rap.)
If i could say that you got kidnapped, I can’t even tell.
(Because of his hat, Dipper can't tell if Finn is kidnapping someone or is being kidnapped, as it looks like a mask.)
My hat looks like a normal one, yours looks fucking weird,
(Just like Finn, Dipper has a hat, but Finn's looks weird to Dipper.)
I’m still wondering, are you and Jake queer?
(Queer means gay, mind you. Dipper is asking if Finn and Jake are gay because of their very close relationship.)
You smell like pork chops and bacon grease,
(This is what Finn smells like to Dipper, exactly that.)
My sister’s pig will give you a disease.
(Mabel Pines has a pig named Waddles. Dipper is saying that Waddles will give Finn the Swine Flu.)
What time is it? Adventure Time,
(Finn is saying his catchphrase, said in almost every episode of Season 1 of Adventure Time.)
Your book is full of glob, now go and get better rhymes.
(Finn is telling Dipper to look on his Journal 3 for better comebacks, because apparently it contains all of the information on the mysteries of Gravity Falls.)
You are not mathematical like the Lich,
(Finn is referring to the main villain of Adventure Time, the Lich, whose mission was the extinction of all life on Earth. Finn is comparing Dipper to the Lich, as he appears to him as uncool.)
If you’re 12 years old, couldn't your voice get the right pitch?
(Dipper has always been 12 years old in the series, yet, he has never had the right voice for it, as in the series he is going through his puberty phase. Finn is also talking about his ability to auto-tune his voice when singing.)
You are always wrong, to rhyme in this song,
(Finn is saying every line Dipper is spitting is wrong in this rap.)
Where is your Mom and Dad? That's right! They're gone.
(Dipper and Mabel were sent to live in Gravity Falls for the summer, but their parents didn't come with them. They've never appeared in the show physically.)
Why is your book always upon
(Stated earlier, Dipper has a book that tells him about Gravity Falls.)
your hat, your dress, your underwear, GET ALONG!
(Finn is pretty much saying Dipper is a mess because he never cleans his room, as revealed in the episode Carpet Diem.)
I would put you and Mabel in the blendy,
(Finn is saying he would put Dipper and Mabel in a blender.)
while I go on a wild adventure with Wendy,
(He's saying that while Finn can't date Princess Bubblegum, he will steal Wendy from Dipper.)
How about you taste Jake’s poisonous spaghetti,
(Finn is threatening Dipper to eat Jake's spaghetti, and is telling him to kill himself.)
Ready for round 2? are you ready?
(Finn is calling Dipper for a rematch.)