Personally, I think "cowboy coding" is the best derogatory name for this. IMO, what all of these ninjas have in common is that they don't realize that software development is a team exercise. Berkeley did a study on BSD and found that a file was opened 10x more often for reading that writing (i.e. people read code 10 times for every time they make a change). To my mind, "cowboy" conveys the proper amount of ignorance of the other people on your "team."
"Cowboy coding" already has a distinct meaning - it refers to writing code as fast as possible without concerns for technical debt.
The archetypal form of cowbody coding is the copy-and-paste: faster than any code reuse technique, but a booby trap for the future.
"Ninja coding", on the other side, refers to coding for cleverness' sake, at the cost of legibility and ease of use. No self-respecting ninja would simply copy-and-paste.
I totally agree with this sentiment. I think it's pretty well established at this point that in many cases clarity can trump optimization. Even more so when the optimization isn't performance based but rather line count based or "code golf" based. Also, do you happen to have a link to that berkley study? I can't seem to find it with a brief search.