Pants/jeans that are too big, like not sagging but just too big. They make you look heavier than you actually are.
White socks with dress pants.
For balding guys, own your baldness. It can be sexy when done right, i.e., cropping/shaving your remaining hair into a very short style (see: Jason Statham).
Please don’t grow your remaining hair long and put it into a ponytail or comb-over or just leave it hanging there or whatever. Please. You’re not fooling anyone.
Jeans that don’t fit right! I see men all the time wearing jeans that are too short or too wide to be flattering.
Please make sure your jeans are long enough!
This is more for younger guys, but starter ‘staches and unruly/patchy beards. I get that you may feel pressure to or want to look manlier, but this is not the way to do it. If anything it brings attention to the fact that you can’t really grow facial hair yet. I know this is hair and not clothes, but I think your hair is a big part of your style. Edit: people keep replying that they’re older and still can’t grow beards, clean-shaven is a great look, guys! Also I doubt anyone would judge you by your lack of a beard, so don’t let it get to you!
Wearing a beanie in warm weather. It makes you look like you smell bad.