Anyone who's spent any time in the corn belt in the fall, after harvest can tell you how prevalent the use of ammonia is as a Nitrogen amendment. Granted, anhydrous ammonia (fertilizer) and urea (found in urine) are chemically VERY different. But when used properly, they can both be used to supply plants with Nitrogen.
Both need to be chemically converted into a useable form in order to be of any use to plants. Anhydrous ammonia is added in the fall so it has a chance to be acted on by soil microbes (among other reasons), which turn it into Nitrate. If it were added at plant, it would probably kill seedlings. Urea is milder, but still needs to be converted.
This conversion is what happens when we combine "green" and "brown" plant material to create hot compost. The microbes in the compost
pile need Carbon (cellulose, starches, sugars) and Nitrogen (proteins, nucleic acids) in the proper proportions to thrive. If your pile suffers from an abundance of brown material (Carbon), it would make sense to add supplemental Nitrogen (urine, or whatever) to balance things out.
However, if your compost pile is composed mainly of lawn clippings ("green" material), adding additional Nitrogen will only throw things further out of balance. Your pile will likely be colonized by microbes that use urea and other Nitrogen-containing molecules for energy (not just as a nutrient source). The final waste product of these microbes is ammonia, which is harmful to plants and will make your neighbors hate you.
So, yeah, pee on that leaf pile! FOR SCIENCE!