recently the car scraped against a building and got some paint scratched on the bumper.
whats the best way to remove it… i dont really want to use some strong chemicals…since it might ruin the paintjob
Chief’s Domain - http://www.seas.ucla.edu/~ravi
Try using a cloth with a bit of petrol on it.
Well WD-40 is recommended for tar removal so that might be worth a try.
I’ve had decent luck with a liquid (vs. paste) car wax. The solvents in that won’t dissolve the offending paint (for which your original paint will be thankful) but seem to get underneath and loosen it.
You’re best bet is to use rubbing compound. As long as you don’t get too vigorous. Since the paint is imbedded and not chemically affixed, rubbing compound should take it off without harming your car’s paint. Of course, once you have shined up your bumper you may have to do the whole car 
Depending on how old the paint is, and whether or not you’ve got a clearcoat, you could try the “polishing compounds” that come in a can. They also make compounds specifically for clear-coated paints. Be sure to get a “polishing” one though, the “rubbing” compounds are much more abrasive and mainly for oxidation removal.
I would try InutilisVisEst’s, RSSchen, and Squid Vicious’ suggestions (in that order). Then, if still no luck, paint over it w/ touchup paint, wet-sand the immediate area to blend the paint (800 grit or finer under running water, very light touch), and several coats of wax since the clearcoat will be damaged in that area.
Just had another thought, media-blasting. It’s like sand-blasting only w/ baking soda instead of sand. I’ve seen a good operator take the printing off a beer can w/o even scratching the Al. But, it’s definitely not a DIY thing. Check custom body shops.
What type of bumper? Plastic? Metal?
Try some soap & water as I don’t know if its plastic or metal.