I am often disliked or dismissed. Even a couple of my best friends didn't like me at first (I found out after we became friends but at least that was a chance to get some insight).
Various reasons I've heard or been able to guess at.
The big one is that I have inattentive ADHD (diagnosed) and suspected ASD (did not pursue diagnosis but my eldest child has both and the consultant who assessed him remarked that I also show traits. Like many women on the spectrum I'm good at masking but my social radar is ever so slightly off wavelength. Unless I know the person well it takes me a split second longer than "normal" to pick up social cues, understand intonation (i. e. Is this person being serious, telling a joke, being sarcastic, teasing me or using a euphemism?) This also makes me anxious and my responses are even more stilted. This seems to make people feel uncomfortable and want to avoid me.
Have terrible resting bitch face, even my children think I look cross and miserable (though they know I'm not and just tease me).
Am quite well spoken and work in a profession known for being well paid. So apparently I'm posh/stuck up. (Am really not.)
Slim, conventionally "pretty" and fairly glamorous. This seems to annoy some people in a "who does she think she is" sort of way.
I'm quite quiet and shy (see comments above), seen as unfriendly, awkward or just plain boring. I also get underestimated at work as there is often an assumption that quiet people are quiet because they have nothing worth saying.
An ardent feminist. Some people seem to be personally offended that I don't use my married name and work FT because I enjoy my career and consider my financial independence important.
My most challenging relationships have been with MIL, BILs and SIL. PILs were quite wealthy and there was always a suspicion that anyone getting involved as a partner was "only after their money". So much so that my husband was the only one of four siblings who married. I always had the feeling they didn't think I was deferential enough of their wealth and importance and should have been more openly grateful that I had (in their eyes) "married up". Youngest BIL in particular was quietly but obviously furious when my husband told him that in fact I earned quite a lot more than him. You'd think he would feel reassured that I had no need to be "after" the family money but it actually seemed to make him despise me even more.
People are strange!