Young lady, I should have you know that Mr. Pennysworth is above wearing "jeans" during his labors in Master Bruce's service!
These are part of a "uniform", consisting of the protective overalls normally worn by your NASCAR racing team pit crews, along with tools and necessary harness for whatever needs the Batman may have. These are carried in an attractive leather (finest Spanish leather, of course) workman's utility belt. All kept humble by a comfortable but dignifying English vest bearing the Pennyworth coat-of-arms.