Definitions

Katie explains what is, and is not, a nuisance:

Things that are nuisances on the subway:
Rats, panhandlers, people who have not bathed recently

Things that are not nuisances on the subway:
Poison gas, biological agents, suicide bombers

I hope that clears things up.

Update: Via Ith, Eric at the Fire Ant Gazette brings us the John Kerry Nuisance Level Alert System.