Like having giggle fits a funeral.
..or telling funny stories about the deceased.
Look, there are many, many people in NYC still suffering the effects of 9/11. This is not a widely-reported story. Some of them self-medicate via liquor or drugs. Some of them have become shut-ins. I personally know hardened NYers who now wince at sirens.
Many NYers are also reminded of 9/11 on a daily basis via added security measures in subways, Wall St. and transportation hubs.