I'm going to get a seasoned manager fired
What did they do that warrants them to be fired?
I want to replace him for doing an awful job not managing his department.
If you think that there is a genuine problem in the department, it is good to report it. You should want to do what is best for the company!
He is the worst manager ever and I hate his guts. I'm gonna complain to the owner of that.
If you think that he is doing a poor job, then I think that it is good that you report him. Maybe the owners are not even aware that the manager is not doing a good job.