I'm wondering if anyone in that situation has asked the question "do your patients often lie about their sexual orientations?"

I'm not even counting the cases of people sneering at virgins for being "unable" to seduce anyone.  I classify that as a separate problem.  

When it's happened to me, it's been people trying to coerce me into entering sexually-motivated romances with random other people, or at least, completely overlook my concerns about entering a romance for what I consider to be the wrong reasons.  On a few occasions, it got worse than that, but I don't want to go into the details right now.

When I've seen it in person, it involved a woman threatening to straddle an openly abstinent man.

When I've seen it online, it's been much worse.  I've seen people claim that if a man doesn't enjoy unsolicited sensual/sexual contact from his romantic partner, that this is a "red flag".  I've seen people claim that abstinent or asexual romances didn't really count.  I've seen people claim that any adult who isn't comfortable having sex with a steady romantic partner is mentally immature.  In one online conversation, when a young woman was venting about her embarrassment that her boyfriend had accidentally seen her completely undressed (and immediately averted his eyes to respect her privacy, but still, we can all understand why that's embarrassing) most people scolded her for being embarrassed, saying that to be in a romance, she should feel comfortable doing more than just showing.

Have any of you had to deal with this? 

I reacquainted with the few family members I now see around 2016. Since that time, and particularly since the post-Covid isolation restrictions, my family keep "jokingly" referring to me having some sort of intimate relationship with a number of people.

The first a friend I used to visit 3-5 times a year. I never stayed at her place, always stayed by myself in a hotel. Most of the times it wasn't even just us, but ace meetups. And my family are well aware that I am generally male-attracted, whereas she was female, and very feminine in appearance.

Yet, my family would imply until a year ago when that friendship terminated (for reasons unassociated to this post), that we were in some sort of romantic relationship. Despite my explaining on a number of occasions that I had no romantic attraction to her, they could seemingly not accept that. Their insinuations continued for a few years, even when I had a boyfriend.

As well as that, there are two friends I have at the autism group that my family suggest I am or may be in a romantic relationship with, despite both of those being in other relationships, and none of us being interested in one another in that way.

And then there are three family members (two steps related, second cousins?) that my family have several times suggested there is something going on. All three are male, none are in any way gay, and two are in long-term relationships.

I only even talk to them every few weeks, one of them not even that often, so I don't even understand it.

They don't make any such suggestions about my two heterosexual brothers, and both have had a lot of relationships, so you'd think that given they are more into the whole relationship/romance thing, that they would be the ones who are always assumed to be in some sort of romantic entanglement with anyone they happen to speak to (I say that, because that is what is assumed of me).

Like, I literally barely speak to anyone, most of it is done online, and I rarely leave my flat, but the minute I say hello to someone, suddenly my Dad and Aunt assume I am having some sort of illicit affair.

They know I am asexual, and that currently my mental health is not even in any sort of condition for me to have a romantic relationship (given I can't leave my flat alone), so why keep making the stupid remarks?