What does an anti-psychotic do to a person who does not have schizophrenia?!

Anti-psychotics are not exclusive to people with Schizophrenia.

It's so difficult to answer such a question, when truly the answer is: It depends.

It depends, mainly, on how the person's body reacts individually.

The medication may very well do you harm, and backfire. However, this could also hold true for someone that DOES have Schizophrenia. Not all anti-psychotics work for all Schizophrenics. If someone's body rejects the medication, then that is that, Schizophrenia or not.
Medication is still very much "guess-and-check" work.
If a Schizophrenic has an appointment with their psychiatrist, the psychiatrist may evaluate the client's complaints, and then prescribe medication based on the symptoms listed and observed. The client then leaves the office, picks up the meds later at the pharmacy, and then gives them a go for a few days or weeks while monitoring the results. Perhaps the medication helped them, and they feel that they need to stick to them. Or perhaps the medication only made things worse, or didn't work at all. If that's the case, the patient then returns to the psychiatrist, explains the issue, and possibly are prescribed new meds to try out.

This goes for anyone. Not just people with Schizophrenia, or even mental illness for that matter.

If someone who doesn't display any sort of psychotic symptoms, then obviously, an anti-psychotic will do nothing beneficial. Will it harm them at all?
Who knows.
It depends.

it depends on which one. The side effects can include drowsiness, dizziness, changes in hormone levels, possibilities of movement disorders (usually in first generation anti psychotics)

This also depends on how much you took

but you will not have schizophrenic like symptoms if you take it when you don't need it, if that is a concern to you.

However, if a doctor has prescribed an anti psychotic to you, most likely you need it, even if you think you don't.

Alsorts of things. There a thousand and one reasons why somebody would be prescribed anti-psychotics when they don't have schizophrenia.

there are 2 classes of these meds, older and newer atypical
the older ones would do harm, the atypical ones would be OK although they can have nasty side effects when started

depends on the med