Hi, I have questions because I don't understand situation. I was shopping with my parents and when we were at the checkout. Old lady looked at me, so I smiled but then she started yelling at me. My mother said that she probably reacted that way because she had a bad experience in past. And it's okey. I can understand that. But moment later this old lady told cashier that I'm laughing at her and even though the cashier knew that it wasn't true she started insulting me with old lady. I don't understand why I always get beaten when I'm nice to someone?
Just a guess: If this is happening a lot in your life, and not just for this incident where the old lady could have had old age mental health or personality issues, and not just where the cashier maybe just assumed wrongly you must have done something improper to her prior, maybe people just cannot read your smiling and gaze intentions, or they just were not in the mood for that at that time. They maybe assumed unfairly a young guy who smiles nicely and broadly is making fun of them, or flirting with them. Perhaps they are not use to this from young guys, or perhaps they just would have not been receptive to anyone that day smiling at them.
In many cases, they may either have prejudices against such persons, or they may have either a lack of trust issue or low self worth or hostile demeanor, or seem wary that such a young guy could be so nice to them without good reason, or as it seemed odd to them to occur from a guy, or at that time. Unfortunately, society can stereotype against such younger guys, in that manner, and think that smiling and friendliness from young males means that person either wants something, or is ridiculing the other in some way, when you were just trying to be yourself, and or to be nice to others. Young guys apparently are supposed to not have friendly manners or show care, but to focus on just completing their business. Or they are supposed to read minds, and do such only when that recipient wants.
Admittedly, in my case, I grew accustomed to not showing smiles or happiness around people, because of my parents, more so than genetics, as whenever I smiled or showed happiness either they would tell me in hostile tone to wipe that grin off your face, or in other instances they argued with each other for other reasons and then instantaneously any happiness from me prior or smiling would disappear anyway. I learned to hide or mask my feelings, and have neutral expression, though for others with certain conditions, certain expressions, whether neutral, happy, or sad, often cannot be hidden, or they can show up supposedly at the wrong times.
Hopefully in your case, you still will not be discouraged from smiling if that is you, or how you feel, or just your attempt to be nice. Realize thus it could be just their false assumptions, for why they think you are laughing at them. They may feel a smiling young male, if looking directly at them, as a threat to them, for whatever reason, whether their trust issues, anger issues, prejudices, or fear issues. I am not sure if neurotypical smiles and gazes can appear different than Autistic, but I do know Autistics and neurotypicals read body languages differently, or to less or more amount.
For instance, I see myself as somewhere in between those with Autism and neurotypicals. I have ocd issues, extreme introversion, avoidance and shyness issues, have particular fascination and hyper focuses, like with regards to sports, writing and music, and am very much into details and am touch sensitive. But, I have a very easy time understanding idioms, figurative language, and how all others could be thinking and feeling, through analysis, as I pick up on people’s nonverbal cues like postures, facial expressions, mannerisms, etc. easily. I even can tell when many others could be masking their true feelings. I can on rarer occasions fib to others too, if the need called for me to not hurt their feelings. I can be less direct thus, during those needed times.
So, with regards to smiling, even if had ability to smile easily, which I do not, I likely would not smile to that other unless I felt that other could be mostly receptive to that. If, for instance, that old lady you mentioned seemed, from my quick analysis through a glance towards her, either not happy, mean, distant, or wanting to mind her own business or not wanting to socialize, even if I was able to smile I would likely be more hesitant to smile at her or gaze at her, fearing that could be unwanted from her. Although most people can see smiles as good, there are times when all people may be less wanting to feel pressure to smile or to be friendly back. In general, in my opinion, if persons seem happier, friendlier, and more receptive to socialize, it is seen as more welcoming to smile, greet, and say hello to that other, etc, though I wish persons could do that to unfriendly looking persons too, without worry of any bad reaction back, as many could be uplifted to better mood perhaps from that good will friendly and smiling gesture.