How old are you? I'm curious because I thought along those lines when I was a younger man. You are right that we have almost no control over our immediate emotional reactions to something we have just observed. You do control your train of thought about that observation going forward.
I'm 29. Yes I agree that you can consciously control what you do long-term in response to something, but you can't just whiff things off entirely.
If someone calls me a "fag", it will bother me whether I pretend it does or not. I'll be offended and it will probably play back in my head for a bit. I can try to let it not bother me, but it probably will at least a little.
"Words can't hurt me" is a fine personal mantra/goal/ideal but you can't apply it to everybody in every case.
You can't simply turn your emotions on and off unless you are a sociopath.