Replying to 811

Does anyone know what this means.

There is a wicked radio show here in toronto in the mornings called the Dean Blundel Show. One of the funniest shows to listen to on the planet. Anyways, frequently the 3 guys who are on the show burst out laughing when other people say 811. I don't get why it is so funny. They will say "Nikki say 811 really fast" and she will and they will fall off their chairs laughing so hard.

If anyone gets it, let me know. Thanks. It has to be something sexual, retarded or peverted, thats all these guys talk about and laugh about. Thanks for the help.