All my life, if a person wanted to do someone harm, their attitude was described as having it in for that person. Lately I have noticed that this has been turned around to having it out for a person.
When and why has this change taken place?
Have it out for (someone) is also used with the same meaning, but its usage doesn't seem to be that common and I cannot find evidence it has surpassed that of "have it in for". Maybe its usage is increasing among younger people. My impression is that it may be confused with a similar expression "have it out with (someone) which has a different meaning and is by far more commonly used.
(The Free Dictionary)