There was never a mention of a hygiene issue. I'm going to just ignore that straw-man argument because I can't see why it's relevant to anything that we're discussing.

It's not unreasonable to ask your partner to be more cognisant of how they present themselves. Whatever reason is behind your request doesn't really matter. If your partner then denies your request, then further insistence that he changes his dress sense is an encroachment on his autonomy.

You seem to think that under certain circumstances, it is okay for your opinions on your partner's dress sense to supersede his opinions. While I'm not necessarily disagreeing with this rather vague contention, the specific scenario we're talking about is whether the OP's opinion of what is aesthetically pleasing can override her partner's autonomy--and that I cannot agree is a valid reason to encroach upon your partner's autonomy.

A male requesting his GF to dress less or more revealing would likely cause an uproar on this subreddit. This is no different to the OP's scenario. In both scenarios, one party has an opinion of how their partner should dress that is not shared by their partner. You can play around with the "nuance" behind the reasoning, but at the end of the day, the fact remains that one person is trying to have their opinion supersede that of their partner's in a matter that is purely within their partner's purview.

If you don't realise you're being sexist, then we'll just have to agree to disagree and part ways.