His response when I pointed out that his way has always been different and always caused him and others more problems until he works through it. Even if his way is infinitely more complicated.
Example: We're supposed to (easy way and TA's solution way) use Solver with a sum of the difference squared error to find parameters in a HW assignment. S2 went out of his way to use Gram-Schmidt and MathCad. No one else is using either. S2 crashed his computer a few times and worked for a few hours to "get it right" and "get it more accurate than any one else's"