Thankfully, I have never been so hard pressed for ferts that I urinated in my tank.
This topic comes up fairly often especially with those that are fairly new to dosing fertilizers. The consensus typically is you can, and are welcome to do so, but your urine also contains a lot of waste (heavy metals, bromine, artificial crap) that isn't beneficial to your plants and/or fish. Since we are attempting to control our own ecosystem to our own design, why would we throw such an unknown into it and throw the whole thing off intentionally?
I do know of more than a few old men who had gardens swore by their secret "natural" fertilizer. They would bottle it for a year or so (by the gallon) and then use it after it "aged" on their garden plants and flowers. I am ashamed to say...this works. The person I learned about it from had the biggest, raspberries in the whole neighborhood. He used it like Miracle-Grow liquid fertilizer. (ironically, he said female urine was no good).
Anecdotally, When I moved into my current house, I had a small black-cap plant (24" tall stems, no berries, about 3"-4" in diameter) that didn't do anything for 3 years. I was going to tear it out, but I decided that I should urinate on it every day after I got home from work. I did this for an entire season. The next growing season the plant took off like never before. That plant currently sits at 9ft tall, 4ft wide, threatens to take over the fence and grows the biggest black-caps I've ever seen.