i know its only an egg but its the principal; to be fair when i was a young lad (16) me and a few mates used to do drive by egging
it could have been a lot worse; 4 big lads could have got out and hassled you with knife's or robbed you etc
i'm not in your position but no doubt i'd be seething too; the longer you leave it the less likely you are to do something - if i'd found the car on the night they egg'd you, i would have slashed tyres!