Is there any way when you assign an opportunity or a lead to a user to have the choice to accept it or to reject it?
thanks in advance
Create a custom drop-down and add the values you want. If you want more functionality based on that field, you can create a logichook to change relationships, reassign to somebody else, etc… all is up to your imagination…
It’s slightly more complicated: if someone rejects it you have to retain the prior assignee to reassign it to him and then notify him of the rejection.
Following AlxGr suggestion it shouldn’t be too difficult to achieve, but you need to know php and how to write a logic hook.
Another way to achieve the same could be via a workflow.