Hello. Could you help me please? I have 2 questions about an special use of "so".

1. In a Huggies' commercial, there are 2 babies talking about the diaper. At the end of this

commercial, one of them says: " I'm so going shopping ".

2. Another one: in the sentence:

Red pants so don't go with a green t-shirt.

Could you explain me the meaning and what function "so" does in both sentences?

Thank you very much.
This is weird, trendy new American slang - "so" adds emphasis, meaning "so very much" or "to a great extent," but the usage and placement in the sentence is not standard English. The sentences mean something like "I'm really ready and determined to go shopping!" and "Red pants really do not look good (or stylish) with a green shirt!" (Please don't try to emulate it!)

I think it derives from the sort of exchange where "do not" or "are not" is countered with "do so" or "are so" -- "You're not going shopping!" "I am so going shopping!"
It's an abbreviation of "so much" or "very much" but its placement in the sentence means that it can be replaced by "really".

As it's a purely colloquial usage, any attempt at grammatical analysis would be wasted.
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Here's my 2p-worth of theory.

Usually, "so" in this sense would act as an intensifier ("to such an extent") for an adjective or another adverb:

1. That's so untrue.

2. Don't be so silly!

3. It was so beautifully spoken.

But in this usage, "so" with "to be" seems to twist part of the predicate into an adjectival subject complement:

4a. I am not going shopping. (subj. + predicate)

4b. I am so not going shopping. (subj. + linking verb + subj. complement)

The "red pants" example has a different effect, to my ears; here, it's a more usual use of "so", but made strange by the nature of the verb:

5a. I love her so. (usual use – state)

5b. Cavies so shouldn't eat sausages. (unusual use – action)

That explanation was way good, Mr. P. Emotion: smile
Thank y'all very much for your explanations. Now I have no more doubts.
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Dear friends,

I have heard older British persons say «I do so hope you can come».

It is perhaps similar. Emotion: smile

Kindest regards, Emotion: smile