I believe firmly in the value of all vulgar notions, especially of vulgar jokes. When once you have got hold of a vulgar joke, you may be certain that you have got hold of a subtle and spiritual idea. The men who made the joke saw something deep which they could not express except by something silly and emphatic. They saw something delicate which they could only express by something indelicate. ..... In order to understand vulgar humour it is not enough to be humorous. One must also be vulgar, as I am.
(G.K. Chesterton, All Things Considered, P.11)
1. Lacking sophistication or good taste; unrefined
* - the vulgar trappings of wealth
2. Making explicit and offensive reference to sex or bodily functions; coarse and rude
* - a vulgar joke
3. Characteristic of or belonging to the masses