Crude humour is humour that is an attempt to describe something as being funny, but in a way that is sexual or vulgar. It references sexual or vulgar topics in an attempt to be 'humourous'.
In some parts of the world, sexual humor in particular is known as "non-veg" humor, contrasted with the "veg" jokes that are more acceptable in polite company. The use of the term "non-veg" is probably a reference to the carnal nature of sexual humor, and can be viewed in the context of the prevalence of both vegetarian and non-vegetarian dietary preferences.