Are you upset that he dresses well now or that he critiques and advises now? If his advice is as stupid as you say, I'd respond with, "THAT DOESN'T MAKE SENSE!" and I'm not one to yell, so it would be humorous frustration. Or you could explain that he just said common sense and mistakingly assumed someone might not be abiding by his minor advice. Just tell him what about his advice is stupid if you honestly feel it is stupid. As far as dressing well, I get that it takes certain attention off you, but you have to know that many of your friends are going to be maturing in style at some point.
WARNING: Unnecessary rant below. Read only for ramblings of someone who hates their roommate's closet's guts.
For example, my tool-bag douche roommate is suddenly seeing all his pledge/frat buddies dressing better and not buying American Eagle exclusively in college. This epiphany of his annoys me for two reasons. Firstly, I have heard him explain his need to buy better clothes to his mother on Skype, and he talks like a dude-Yo! type as he says that his style has matured and Lacoste is going to be his grown up American Eagle. Second, my closet is full of the stuff he is telling his mom he needs to get now (though I opt out of logos, so Lacoste is at a minimum), but he didn't realize until days ago that his American Eagle filled closet next to mine looks tacky, obnoxious, and most definitely middle/high school. He also says he needs Sperry boat shoes (which I don't wear because I don't like them) because everyone has them, so naturally, he has to wear them. Not because he knows how to wear them or wants them.
As you can tell, he sucks. But I keep it in, so he keeps assuming I am his pleasant, clean, quiet roommate, while he leaves nasty stains on the counters, his sheets, and his dirty clothes crawl on the floor towards my space. Or so I hope he sees the differences between us in this way.
I never knew I could hate the word "Yo!" so much until I started living with him and learned that he answers his phone every time with the word, as well as to get my attention to ask questions. He is in the room as I type this, so I am having trouble explaining what is so funny, but it is really just my evil judgments pouring into Dappered Threads.
P.S. - He owns the ugliest custom Converse shoes that have yellow laces and interior, teal main colors, and red accents. Disgusting clown shoes.