INTjs are described as being somewhat dull, solemn, and serious. Othertimes it seems as if we are described as being humorless robots. But my question is how do INTjs typically exhibit humor and to what extent? And does this differ or compare to other alpha quadras? I know that generally INTjs like to pretend that they do not have a sense of humor and that slabs of granite are more likely to laugh before they do, but I don't think that is necessarily the case.

The reason why I ask is because I read the description of the INFp on Socion.info and their approach to humor is very similar to mine despite being a strongly identified INTj.
INFps are distinguished by their sense of humor. Their humor is spontaneous, cutely ironic, and oftentimes rather random. They may put on a faзade of being under the influence of any number of substances, and as a result may appear childish, out-of-touch, and spacey. This is actually a defense mechanism to distance themselves from a contrived existence. When acting like this, they are most likely thinking: “You people take yourselves way too seriously.”
This section is where a portion of the similarity exists. One of the differences is that I am less "cutely ironic" and more "bitingly ironic." And it only seems like being rather random because it is in stark contrast with my usual behavior. My humor also developed as a defensive mechanism, but not to distance myself from a "contrived existence," but due to my idiosycrancies. But the last bit about "You people take yourselves way too seriously" is in fact one of my primary motives. I have been told that my humor "makes people feel uncomfortable but in a good way." But by doing so, I do not hope to get people to be more relaxed or easy-going, but to get them to open up and make it easier for me to learn about people and to "expand their horizons" in regards to societal behavior. In other words, there is generally method to the madness.

They may seem estranged from reality, but they in fact dwell on a far more significant plane in their own minds. Internally they understand full well the gritty undertones of life, but see the world within the context of an overarching, transcendent framework that liberates him from the trappings of the workaday world. They have their eyes on “bigger issues” at hand.
The main difference, however, is that I spend my time in a world of logistical theorization and not a world of the INFp.