I understand that smiling makes me seem submissive, but why should I never smile?

I only ask because I spent the last two years in school "mean mugging" everyone and everyone thought I was an asshole, that I hated everyone, and it made me look tired. Yeah, sure some girls thought I was attractive, but my mood and personality had skyrocketed when I started to smile a lot more. Simply smiling makes me less stressful and more happy, which gets rid of any negativity I've been feeling that day. Maybe it's all in my head, but smiling has made me more approachable and better in group interactions with other people.

So trp, why exactly should I avoid smiling? If I can smile, what situations should I not smile in?