If someone was to walk around in just boxer shorts would that be in violation of the law? If yes, then there are a lot of runners I see who probably would be in violation of such an ordinance. If not, then how can wearing your pants so low that you can see someone's underwear be against the law?
What should be against the law is white people wearing their hair in dreadlocks. It is just wrong (though on African-Americans it looks great - it is just never works on a white folks).
Other things that give greater offence than low pants with boxers exposed:
1) Crocs shoes worn with socks
2) men in capri pants
3) tattoos on the neck
4) shaved heads on white guys (usually, some can pull it off)
5) ball caps being worn in restaraunts
6) man purses
7) others? . . .
Once the city of Atlanta gets these issues solved, which IMHO are far more serious, then they might begin on the low pants/visible underwear thing.