Certainly not offensive, just seems like it indicates that a school's priorities aren't necessarily in the right place IMO. Personally I'd want my students to feel free to dress however they want (within reason) when they are in preclinical years--which is basically glorified undergrad anyway--and allow them focus on learning. As long as you show up to patient-related situations dressed appropriately that's really all that should matter (not to mention most medical students dress more formally on the wards than many attendings).
Then again it clearly doesn't bother many of you so keep on keeping on.