I am ugly!

I think this phenomenon is the result of having a really strict idea of what an acceptable smile is

I reckon it’s probably to do with internally trying to downregulate the smile so it doesn’t look really weird or crazy or fake or stupid and you just overcompensate. You don’t know what you look like while you’re doing it and that information void gives rise to some self consciousness and pre-emptive embarrassment. Natural smiles don’t require you to think about how to do it at all so most people don’t really know how to smile in a socially acceptable way on demand with a few seconds notice. Some people are better at it than others, maybe they have a better intuition, maybe they have a better awareness of what muscle movements correspond to what changes on their face and also a really good grasp of which tiny subtleties lead to a photogenic smile or the grimace of a maniacal murderer. Actors are probably pretty good at it either through intuition or just a lot of practice. I should imagine you could train yourself to be better at it, but it’d feel weird and vain to spend your time doing that so a lot of us just make weirdly flat or stern faces in photos.

If you can actually just enjoy the moment so it makes you smile as a result it’d probably get better results but that idea leads to its whole own self reflexive internal monologue trying to concentrate and force yourself to be happy that probably results in a frown while you summon that concentration.

I always feel like I’m over smiling to the point of absurdity but I look normal and people respond positively. My natural state is not to smile so I think sometimes it just feels weird when I have to force it

All the time man

Are you perhaps introverted, with a bit of social anxiety? Are you subduing your smile (maybe subconsciously) so that you won’t get teased for overdoing it?

Also maybe try practicing by smiling (or what you think is smiling), then without changing, open your phone’s camera and see what you’re up to. Then try to remember how a good smile feels.

I have the opposite problem. I feel like I’m smiling a nice decent smile, but then I see I looked totally maniacal.

Yes, this happens all the time to me. I think it’s a relatively common thing for autists to emote differently, and I’m autistic, so I guess it makes sense for me. People who know me well can definitely detect my smiles though, so that’s nice. I’ve been trying to get used to overcompensating for strangers to make sure they see my expressions, and I just hope that it doesn’t end up looking too uncanny valley.

Because we can feel even the most minor movement of our facial muscles away from our natural resting position, in much greater precision than what other people can see of the same.

Yes! In fact the only times I’ve seen myself smiling in a photo is when I’ve intentionally done a laugh

I always try to think of something funny to get a natural smile. Otherwise it just never works.

Personally; no, but I have a resting ‘nice’ face. My partner does have this happen to him though!