“Goosebumps walkaway is the line that the guy says to the girl in the movie that gives her goosebumpsand then he walks away forever,”
Nick is having a hard time saying goodbye to Reagan, too, and keeps saying the wrong things to her, so he devises a plan to act out a goosebumps walkaway to up his cool.
A Wallaweeb is a derogatory term for an outsider who obsesses over Australian culture. The name derives from "Wallaby" (a small, Kangaroo-like creature found in Australia) and "Weeb" the shortened version of Weeaboo (an outsider who obsesses over Japanese culture).
"You know, Vegemite is genuinely phenomenal. You just have to develop a pallet for it."
"Steve, quit being a wallaweeb. That crap tastes like spicy toe jam."
The "goosebumps walkaway" is the moment a man says something to a woman before he walks away, something so deep that the woman in question gets little goosebumps on her arms.