My least favorite engineering character is unquestionably lower case zeta.
In vibrations, this little guy is the damping ratio. Why don’t I like this character? I guess there are two reasons. Firstly, it’s really tough to draw. Try it. At least for me, it took a bit of practice before it stopped looking like a random squiggle and started looking like its true Greekish form. Secondly, it’s not as widely recognized as, say, the ampersand. That means, that if you screw up in your artistic attempt to draw the little guy then no one will have any idea what you’ve written down.