I know I'm late to this, and honestly it's been a while since I did any serious physics or math, but does it really bother people more that a German double s is being used for a variable than someone is trying to subtract "i", the imaginary number equal to the square root of -1? You can't use "i" as a variable because it is a number. "x", "y", "z" etc do not have an assigned value, thus they are variable, but "i" is defined, in math terms. And it can be used to multiply or divide, but I don't think you can subtract it (or add it for that matter)

AND often it is thrown in just to make an equation work, which is how it is used here, not to make it work mathematically, but to make it work humourously.

I like TBBT because I know some of those people. My wife tells me I am one of them.