I'm sorry - I can't relate to such a thing at all. There's something about even the concept that smells of power play. No one has the right to have any "veto" over another human being unless they are a child or otherwise incapacitated.
In a good, caring relationship there should be no need. As long as people are talking beyond hello-goodbye.
To me a preferred method of handling possible disagreement or conflicts is simply to express my/your feelings and concerns, provide facts to substantiate where the concern comes from and let the other person make their choice based on this. If they choose to ignore the concern - they are responsible for the outcome - including deterioration or destruction of the relationship.
By way of an example............
You want to do X
I'm uncomfortable with that. I tell you why. It may involve safety etc. I may have insight you are not aware of. YOU may have info I am not aware of.
One we have all the facts in front of us so both are at the same level - you still choose to do X
I lose respect for you, our relationship and may develop real concerns about your judgment.
You proceed to do X against my recommendation
It turns out well
I learn something, about myself, about your judgment etc.
I'm big enough to admit I was mistaken, have learned something, and we become closer
No power dynamics required.