Learn English – pronoun agreement in neither nor

...and try not to be shocked or overreact if...

In this sentence, you're telling them that what they must try to avoid is any of being shocked or overreacting. In essence, you're asking them:

...[try not] to [either be shocked or overreact]...

And not, for instance:

...either [try not to be shocked] or [overreact]...

Phrases with neither...nor are more explicit, but also more formal, and I think not...or is much more common for lists where all items are negative.

When subjects are connected with neither/nor, the one closest to the verb controls the agreement. Thus, neither you nor I am. Why? Because lots of English grammar books say so.

Sounds awkward? It does. Lots of other English grammar books agree and so does actual usage. As you can see, there's an actual controversy here. There are workarounds that would please adherents of both viewpoints. The easiest one is probably neither I nor you are, but most of your proposed variations would work.

Of course "*Neither you nor I is" is totally wrong, because is doesn't agree with anything in this phrase.