It is a silly sentence, it is not grammatically correct but that is part of the joke. Friday is a noun, but this sentence is also using it as a verb and an adjective. The meaning I get from this is kind of "this Friday is such a typical Friday that it is the most typical Friday that has ever existed as a Friday". I hope that helps!

it's nonsense. It is someone being silly that they like Friday probably because when the work day or school day is over, the weekend starts.

Not standard English, but understandable.

Fridays are usually the start of the weekend that connotes freedom from work, stress and lack of fun. So Fridays are used to describe the start of a fun weekend. So “fridaying” basically means having lots of fun since it’s the start of a weekend.

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