Why can't stress pronouns be used in the singular?

Question

Laura K Lawless · Accepted Answer

Bonjour Chris,
Sorry for the late response. It can't be singular because they are two different people talking.
John: Nous sommes arrivés ! (Linda and I)
Alice: Oh non, pas vous ! (not the two of you!)

Chris Wilson · Answer

The question was "Nous sommes arrivés! - Oh non, pas ___! (We've arrived! - Oh no, not you!)" I answered with "Toi" (ie in the singular) but this was marked as incorrect with "Vous" given as the only right answer. If you could explain the problem with Toi, I would greatly appreciate it. Thanks

Chris Wilson · Answer

I have to say that it wasn't at all clear that the "oh non, pas..." was a reply to the people saying "nous..." I had thought it was a continuation - hence my frustration.