When should I use "pissworm"?

Why would he say that summarizing experience is unnecessary? Doesn't the point of writing a resume is to shorten one's entire career?

You're right. It is technically a summary! But, he's emphasizing the importance of it making it sound or appear good rather than just a list of things. It's about how the summary is delivered in a way that "sells" it! Ex: Don't just read the book to me, make it come alive! => Meaning to make it more interesting than just reading words on a page. Add emotion and depth. Ex: We're not writing an advert. We're selling a product! So what would make consumers interested in this?

What does "giganda" mean here? It does not show up in the dictionary.

A "giganda" slice, normally spelled "gigante" after the Italian word meaning "giant", refers to a giant or very large slice of pizza.

What does “nick” mean here?

In this context, "nick" is an informal verb that means to "steal." Ex: He nicked an expensive watch from the businessman. Ex: He was caught by the police for nicking small items.

Is "treasure" used as a verb here? Can "treasure" be used both as noun and verb?

Yes, "treasure" is a verb in this context. When "treasure" is used as a verb, it means to cherish, adore, keep safe, or value a person or an object. Ex: I will treasure these photos forever. Ex: He treasures his wife dearly.

Why is it "in there" instead of "in that"? I thought the object they're talking about is definite so "that" sounds natural.

"In there" is used here rather than "in that" because the object in this scene is hollow on the inside, making it an enclosed space. Because it is an enclosed space, it is considered a "location". Therefore, "there" is used because "there" refers to a location. "Get something in there" is also a standard phrase native English speakers use. Ex: Will you help me put my jacket in my backpack? I can't get it in there.