They both thought you were badass.

Most likely because you were an actual teen... but also because you hung out with them.

Dipper even talked to you about the things he'd seen and read, and you believed him, which he's very happy about.

Mabel is just endless excitement around you, because she knows you can most likely handle it.

It was another day in the Mystery Shack.

Ford in the basement, Stan stocking shit and overpricing it all, Wendy just chilling, Soos going around cleaning, Mabel playing with Waddles and Dipper reading up in the journal he found in the woods.

Suddenly, Mabel went into the living room where Dipper was.

Mabel: Dipper! Look at this cool new trick I taught Waddles! Roll over!! She stated excitedly, as Waddles snorted and rolled over, he was a cute pig.

Dipper: He wasn't paying attention all the way. Uh-huh, that's cool, Mabel. His tone was unenthusiastic and focused.

Mabel: You didn't even look! She mumbled, annoyed. But then she looked up at you, because you just so happened to be there too. (Y/N)! Did you see Waddles' trick??