I have noticed most of my coworkers will not say you're welcome. Then I realized I'm the only one saying thank you, lol. I wonder if it's uncool, or ppl don't know how to show appreciation, or how to be polite. I'm told that I'm too nice. Idk. It's mistaken for a weakness. Just who I am, why should I change. Oh, BTW my boss/lead will call us slow, stupid, announce our mistakes, laugh about spanking and whipping us... I feel like I'm losing who I am being around negative people. While it's possible to be too mean. Too rude. Too negative. I don't think anyone in the world can ever complain about being too nice

Absolutely nothing wrong with being nice. I know I have to do it when I'm not expecting how the other person is going to respond, otherwise I can be taken aback by someone who doesn't appreciate it or ignores it. Just to keep in mind that everyone's going to respond from where they're coming from. Of course, there may also be some nice responses. But it's all part of the deal.

Yeah you can be too nice, but there's no simplistic way to thread that particular needle.

It gets easier as you age, because it's easier not to give a fig what others think. It's all over but the shouting and you have little or nothing to lose. Maybe pretend you have 5 or 10 years to live and act accordingly? I dunno. I think though that on balance we are too accommodating, too concerned about what others think (or more accurately, willfully misperceive) about us, etc.

There's a balance to be had between compassion / empathy and not suffering fools gladly, and I'm still always seeking it, but as life has ground on, I have tended to move in the direction of increasing BOTH. That is, increasing my capacity for forbearance and loving kindness while also increasing the strength and definition and number of my healthy interpersonal boundaries. There's nothing incompatible between being understanding of asshats, and not subjecting yourself to them.

One needs to know whom to be nice to and whom to ignore. Or just up your meds.

I don't think it is. I hope people are not as stupid, ignorant, and close minded as they seem to be, and while they use underhanded tactics in an argument, I cling to the belief deep down they realize they were not fair or honest. If I'm right, your behavior will win out, even if you don't see it. If I'm wrong, then you don't leave the argument feeling low or dirty for slinging mud like they do. Only politicans seem to be a profession where doing the dishonorable thing pays off...and who wants to be one of those?!?!?