Resolved questions
Have you ever used wish in this form:I wish I wouldn't have seen you.

You can use wish in the present and in the past; so :

A. 1. We use wish + past simple to express that we want a situation in the present (or future) to be different:
I wish I spoke Italian. (I don't speak Italian.)
I wish I had a big car. (I don't have a big car.)
Future: I wish it was the weekend tomorrow. (It's only Thursday tomorrow.)

2. We use wish + past continuous to express that we want to be doing a different action in the present (or future).
I wish I was lying on a beach now. (I'm sitting in the office.)
I wish it wasn't raining. (It is raining.)
I wish you weren't leaving tomorrow. (You are leaving tomorrow.)
B. Wishes about the past
We use wish + past perfect to express a regret, or that we want a situation in the past to be different.
I wish I hadn't eaten so much. (I ate a lot.)
I wish I had studied harder at school. (I was lazy at school.)
C. Wish + would
We use wish + would + bare infinitive to express impatience, annoyance or dissatisfaction with a present action.
I wish you would stop smoking. (You are smoking at the moment and it is annoying me.)
I wish she'd be quiet. (I am annoyed because she is speaking.)

See http://www.eslbase.com/grammar/wish to know more about wish

Hi Maria

I wish I had not seen you today/yesterday etc
(In every day conversation "had not" is written and spoken as "hadn't" )
I wish I hadn't seen you today/yesterday

I wish I had not met you today/yesterday etc
I wish I hadn't met you today/yesterday etc

As an native English speaker I also notice when words look or sound strange to me!

Hope that helps...

All the best,Morgan

I wish I never met my x-wife! :)

You can also say: I wish that I had never laid eyes on you

NEVER!