OP didn't laugh at her though, she just observed that some older women appeared to be laughing at her. What's she supposed to do about that?
And going up to the woman and asking her why she's wearing a thong would be unmannerly and intrusive, and no one on this thread can do that.
Yes, as a feminist, I think the world is better with less misogyny. So I think it's important to discuss and be aware of the way that patriarchal and misogynistic socialisation shapes our choices, often in ways we're not consciously aware of. How can you combat misogynistic behaviours and attitudes if you can't identify the subtle and insidious ways in which those things can seep into society?
For instance, someone might claim that sexual strangulation isn't a feminist issue, and the world is better if we don't think or talk about it, and we shouldn't judge women for wanting to be strangled...but in reality, sexual strangulation is a sharply rising trend driven by porn, which causes real and serious harm to many women, and the mindset of a woman wanting to be strangled, or a man wanting to strangle a woman, is something that I think should be talked about.
Obviously I don't spend all day every day thinking about it, but it makes for interesting and valuable discussion.