Where did you get the sentence from ?

Impératif mustn’t have any subject, Toi can’t be used with an impératif form.
Neither for Infinitif, because Impératif and Infinitif are both different conjugation.

Knowing that, the first sentence is grammatically incorrect. You can still see it sometimes for example it is the form used by Tarzan. If it is your sentence, use instead “Ne reste pas dans mes pattes.”

Toi pas rester dans mes pattes.

This is an ironic structure, where the idea is to simplify the structure to be sure the other person will understand what you mean (the use of infinitive is the easiest form of a verb, right ?). So you will use this kind of structure when you are talking to someone who don’t understand your language.
When talking to someone who speaks French well, this is rude, implying “I’m lowering my language skill to fit yours, so you can understand me”.

You may also add a pause between each part of the sentence, as if you were expecting him to need time in order to parse your sentence and understand it…

Toi…. pas rester… dans mes pattes

On your side note [1]: (I didn’t understand the difference you make between “saying again” and “repeating”, but I’ll try to explain anyway)

Je reprends

Here, “reprends” should be understood in the context of pause/resume (on a DVD for instance), with the slight difference here where you’re not only continuing your chapter, but you also came back to the beginning of it, and change the language settings.

You may also hear it when a teacher is giving a lesson, then a student interrupts her, so the teacher stops her speech, answers the student, and says “bon, je reprends…” to continue where (s)he stopped.

So the idea of “repeating something I said” is not mandatory, it’s a matter of context.

Edit: Eau qui dort gave us a very nice rephrasing:

“Je reprends” also means “Let me try again” in this context. “Je reprends mes efforts pour t’expliquer” in other words

On your side note [2]: Indeed, that’s the idea.