Ways you can say - I Disagree

No

No Way

Bad idea

Forget it

Go to hell

I disagree.

Consider this:

That is crazy.

When pigs fly.

I do not agree.

Not on my watch.

That is absurd.

I beg to differ.

When donkeys fly.

I do not think so.

You can’t be serious

Not in my life time.

I do not agree at all

Not no, but HELL NO!!

I’m afraid I disagree.

When hell freezes over.

Are you out of my mind.

I sure as hell hope not.

It's not going to happen.

I’m sorry, but I don’t agree.

If I could voice my opinion here...

I see where you're coming from, but...

With all due respect, I've always thought...