A Dupont Circle coffee bar has a cautionary tale for any small business that enables WiFi filtering offered by its internet service provider.

In the case of Emissary DC, the result of selecting the filtering was merciless trolling by followers of alt-right provocateur Milo Yiannapoulos.

The WiFi at Emissary DC in the 2000 block of P St. NW is is provided by Comcast.

Comcast has a button customers can click to filter out offensive content like pornography and white supremacist hate sites.

The owners of Emissary DC enabled the service.

On Sept. 12, Yiannapoulos made a Facebook post claiming his website was being blocked by the coffee shop.

Yiannapoulos has three million Facebook followers. So many of them trashed Emissary DC with negative reviews that Yelp and Google both stepped in to moderate.

Comcast says its content filtering is provided by Norton ConnectSafe.

The owners of Emissary DC say they did not specifically block Yiannapoulos.