I think the term surrealist is frequently misused to describe horror and black comedy created in comic form. As Muz points out, Vasquez is not a surrealist but a lot of people label him as one anyway.
It's worth emphasizing that psychotic or fucked up art is not automatically surrealist. As Dali himself says, surrealism is not an embrace of madness. Surrealism is about exploring or expanding how we think or how we interpret the world by taking familiar elements and associating them in unconventional ways. Good surrealist art comes from juxtaposing disparate concepts or realities and resolving their conflict in a way that produces a startling or thought provoking result. It's more than just a random brain dump, and it's interesting not just because it's incongruous or fucked up. The genius of surrealism is the use of simple incongruity to make a more profound statement, provoke a question, or put a spark in the mind of the viewer.
A very simple example is Dali's Face of War noting that the nature of war is an endless cycle perpetuated through images and speech of death and of previous wars.
A more elaborate example that really illustrates the genius of surrealism is Magritte's painting Key to Dreams:
At first glance, it's deceptively simple. It looks like vocabulary flash cards with an obvious incongruity: some of the words don't match the images. Many art school interpretations superficially follow that lead and explore the statements it makes about semantics in discourse. Some who have a preference for the word form suggest it illustrates that the meaning of symbology is undefined except by convention. And some who prefer the image form discuss the arbitrary nature of the labels we apply to things. But more generally, it suggests the meaning of any semantic representation is contextual, the meaning of something is established by relating it to something else according to convention, and thus the basis of knowledge is not truth but metaphor.
While those interpretations are valid and interesting, the primary meaning of the painting is given away by the title. It's a commentary on Freud's The Interpretation of Dreams, a critical commentary I think. The frame around the images is actually a window, with a dark background signifying the night, and the images are abstract symbols for the things we dream about. It's a metaphor for Freud's belief that dreams are a window into the subconscious that can be accessed by condensing, compositing, and then interpreting the images from our dreams. The words represent the non-literal interpretations that Freud's method ascribes to the dream symbols. On one level, the painting speaks to the arbitrariness and futility of Freud's interpretation method. Beyond that, it challenges Freud's basic assumption that dreams are the basis for accessing the subconscious, because surrealists believed instead that techniques such as automatism were the keys to unlocking the subconscious.
Sorry to ramble for so long. Don't even get me started on Dali's Galatea of the Spheres.
Anyway, the point I was making is that surrealism is not simply a celebration of the random and absurd. Good surrealist art should be mind-expanding, or at least aspire to it, and David Firth's cartoons don't do that for me. Even though he may be using some surrealist techniques, the end result seems like pointless entertainment. Whereas Magritte's work can be profound on its own, but it's real gift is that it's a jumping off point into philosophy. Similarly, Dali's later work is a jumping off point to explore the relationship between humanity, religion, and science. Putting Firth into the same discussion is like putting John Lily and Allen Ginsberg in the same camp as the kid who uses LSD to trip out at a concert. And I'm insulting the likes of Dali and Magritte by even making that analogy.