I am pretending to write something down.
In this scene, Mabel and Wendy are having a "random dance party for no reason!" and Dipper discreetly attempts to opt out. While this may be due to his embarrassment of the Lamby Lamby Dance, I have a different theory. I think that it's because of his crush on Wendy. As shown in Double Dipper, Dipper is nervous around Wendy, and could not ask her to dance even when the moment was perfect.
I like your moxie, kid.
In some shows, one side of a crush is totally obsessed and the other side is either really dumb or doesn't care. Not Gravity Falls. Dipper and Wendy are good friends, even with Dipper's crush, and the feeling is mutual. It's unknown just how much Wendy likes Dipper, but it is known that it's a lot. Wendy seems to consider Dipper one of her best friends, just like Mabel; although, not much is known for sure.
Is this a leap year?
Sorry kid, I ride shotgun, alright?
Robbie's seemingly innocent comment could have some major implications. He likely has built up his status among this group of friends. Some of this could be his closeness to Wendy, who also seems to have a high status in the group. This could also simply be to show the beginning of Robbie's rivalry with Dipper, as well as to foreshadow his future relationship with Wendy.
Zombies rule (right next to ROBBIE!)
This inscription is on the roof of Thompson's car. It is in the front of the car, where Robbie has just stated that he sits. This seems to back up the theory that he is a zombie. This theory is further backed up by Robbie's appearance, his profession to be a teen, as well as his pale skin and bad attitude.
Muffin in the car
Robbie's explosion muffin appears in Thompson's car. It may not mean much, but it shows that he likely practiced there before drawing the design on the watertower. The design also appears near the foot of the watertower, on the fence, in the episode "Fight Fighters".
barbed wire over the fence
Dipper-adult image
Whatever it is, I'll do it! - Thompson
Shows that Thompson is the risk-taker in the group, ready to do anything for a laugh or a buck. If Gravity Falls comes down to some kind of all-out battle, this could be a powerful asset.
Flavor pups
The flavor pups in Mabel's hallucination say two things: the first says what sounds like gibberish, and the second says "Would you like to eat my candy paw?" But the first pup's gibberish line, played backwards, sounds like "Must distrust Grunkle".
Yes, yes I am.
Phineas and Ferb reference!
