Car damage

Car polish would be my recommendation.

If you cannot get hold of any pro scratch removal stuff, try some soapy warm water if the paint hadn't adhered completely or, at your own  risk, try some nail  polish removal lightly rubbed against the paint if small area. Don't forget to ask permission from your missus. Good luck!

Don't worry, it should come off without damaging the underlying paint. You could try just gently scraping it off with a fingernail, or one of those kitchen scrubbing pads (not the metal ones like Brillo).

I tried with a finger nail without much luck - it is probably doable but it would take forever. There is enough of the stuff that I should be able to test different methods. 

Don't know if you can get it you live, Sniper, but I would use T-cut.  This liquid is very effective at removing minor scathes and blemishes without damaging the paintwork. 

Lighter fuel (petrol) with one of the items tonym is on about.  Might dissolve the polish that must be between the two paints.  Good luck.

If you use T-cut or a solvent finish off after removal of the paint with a good polish.

Good luck.

Google Magic Eraser.

Flash sell them in the UK. They are magic.

EDIT.

Just read the packaging, recommends not to be used on vehicle body.

Be careful using T-Cut on metallic paint. It has a clear lacquer on top which the T-Cut will partly or completely remove. Then the car might need waxing and re-waxing regularly to disguise the patch. 

Brasso and then give the paint a polish with car polish afterwards.

Brasso is good for this.

It is milder than T-cut, and can be used very gently to avoid taking off the metallic paint and the lacquer that will be on top of it.

It will be extremely difficult, however, to avoid some damage to the lacquer. If you can possibly get an expert to do it then do so as such a person will have far more experience at getting this right.

ATB from George

Silver metallic could be covered with a transparent coat just like diamond black on bmws. I would call my friend and tell him the story. Then i would get a date with a prof autobody. Maybe for some coins more you can get the whole car fresh polished. That would be great.

If it's a modern car - don't use T-Cut or Brasso,

they're far too harsh and can very easily damage and change the tone of the shine.

Wash the area of concern with car shampoo using a microfibre cloth.

Use some clay bar - it's hard work but it won't do any harm and the results are fantastic.

Finish with another shampoo wash, then wax.

This is good...

Also, buy a latch for that gate ; )

Debs

I would clay it. If this doesn't work consult a professional. 

Blu Tack followed up with some green paper

Green paper?

If it is a really nice/expensive car I would consult a professional.  I don't know how available that is given where you live, but any approach may land you there anyway with today's clear coat paints.  Just have that on the ready lest whatever method your try to employ leaves a noticeable remnant of your attempt.

OTOH, going there straight away may actually save you inasmuch as they can expertly do something on the affected area that doesn't affect anything, and a failed amateur attempt could lead to the entire vehicle needing to be addressed to even out everything.

 I feel your pain - sounds like something I would do...

The funny thing is my friend did a similar thing himself and I laughed at him. Serves me right then. Pro paint shops are hard to find here and being 'multi-millionaire' foreigners we will get shafted on the price and maybe the quality of work too. Such is life. The clay sounds promising. 

Some ridiculous ideas offered here, some of which will definitely damage the paint on first application.

Try Autoglym Super Resin Polish first. It's a finishing polish, but contains a very mild solvent. It's expensive, but would be my first attempt.

Similar advice to others offered above.

Firstly wash the side of the car with car shampoo; rinse; and dry with a non leather chamois/ micro fibre cloth.

If you already have car polish, apply a small amount to a clean lint free polish cloth and work into a small area of the paint marked area to establish if this will be sufficient to remove the black paint mark.  If it works, continue and apply the polish to the whole side of the car - otherwise it will look very odd first time the car is washed or left out in the rain!

If it doesn't work I'd go for the clay bar route - Meguiars used to do a Smooth Surface Clay kit.  Important thing with clay bars is to use them in association with a specific lubricant - Quick Detailer in Meguiars case.  That should remove the marks.  Then apply polish as noted above.

If that doesn't work you could consider something like T-Cut but as the car is not yours, my advice would be to take it to a body shop where if you talk nicely to them they may well sort you out with one of their own brews.  Hope that helps.

Peter

Now there's some lateral thinking! 

Yes, and if your friend really "loves" his car as you have intimated, advise him to seek some professional help.

It could be a princess?