where was he when you reversed? passing by the top looking for a space, or parked himself...?
because you may have been 'nowhere near him' when he beeped, but maybe he thought if you continued reversing you would have hit him if he hadnt alerted you - you were presumably moving towards him.
he cant have been that far away either, if he and a bystander both felt you were wrong...can he?
i daresay his version of this - and the bystanders - would be very different - and i notice from your OP that you seem to have a problem admitting what you did and decribing the situation properly - lots of wishywashy non-committal phrases like - "it appears that i may have appeared" and "i may have told the bystander to f-off" ... you either did or you didnt...!
instead of just saying what happened, you think wording it this way makes it sound like you are less guilty - it doesnt...
so i suspect the situation was a bit more heated that you are letting on - the fact that a compete stranger felt the need to butt in, and the fact that you went over to confront him first "for staring" and said -your words - "whats your problem?" shows you were the one with the bad attitude and spoiling for a row.
his 'problem' was that you almost backed into his car and probably frightened him! - and then instead of waving a polite apology you jumped out in an agressive manner and started an argument...
from what you say, it was you that behaved badly...had he really been the one with the attitude he would have arrested you and caused you a lot of trouble...he didnt... he actually let you off with a simple warning...
i am amazed how everyone here is accusing this policeman of being a jumped up power mad jobsworth - when he didnt even do anything!
he just warned this guy - who has admitted being aggressive and threatening - to back off or he'd be in trouble...!
who knows how far you would have gone if he hadnt flashed his badge?
id have flashed my badge too if it made you go away!
i think you got off very lightly... if id have been him and youd almost hit my car then stormed over kicking off - id have had you in the cells...
that said...this won't affect your studies or job - if you have told the full truth - (ie, you didnt almost appear to may have punched him or possibly may have kicked his car...) - then arguing with a police man will not appear on a CRB or a record.