Well, I think it makes no sense to fire any coach after one season. It is only fair to give a guy at least 2 years. Plus, you're only insulting your own decision-making ability ("He's so bad you don't even give him 2 years? What kind of idiot were you for hiring him then?) if you oust a guy after one year.
First year records
Jimmy Johnson 1-15
Bill Belichick (Patriots) 5-11
Chuck Noll 1-13
Bill Walsh 2-14
Bill Parcells 3-12-1
Unless there's some colossal screw-up (ala Ben McAdoo, and we're not even all of that was completely his decision), one year is just not enough time to evaluate that job IMO.