How ridiculous and jarring would it be if one of the band members here was in a t-shirt and jeans, with a truck driver cap on?
I mean, it's already kinda' ridiculous, but that part is intentional : p
If a band wants to portray a certain group image, either go along with it or get out. You all should generally be on the same page with things like that. In this instance, I'd suggest that you leave if doing things like dressing a certain way bothers you
Also, you shouldn't be slacking on performances.