iRL, I'm a asexual demiromantic, which is a concise but fancy way of saying "I have zero interest in mashing squishy bits together with anyone, regardless of what bits those are, but I can still feel romantic attachment to people based on an emotional connection".
And in the past few years, I've played different characters with a wide variety of sexual preferences that don't match my own—although admittedly way less male characters than I used to—but it's almost never been a problem, as their sexuality is often not super key to their day-to-day RP. (Save, admittedly, for one character who was bisexual but internally terrified of making emotional ties to anyone, because then she'd feel anchored in one place and unable to pick up and run if she had to. So she played it off as 'I just have fun' and had a rule of "I will sleep with basically anyone once, and never a second time." And for that one character, the strings-free on-a-whim once-only sex with anyone was actually a fairly key part of her never-let-anyone-too-close characterization.)
There's only one situation that really stands out to me where someone was terrible to me about my character's IC sexuality (on which, more later).
However, I have a friend who ends up playing trans women fairly often when the setting allows for it; and wow do they get some flak for that choice in various places. People are like, "This is an imaginary character, why would you do that to her? Just make her a woman outright." "I'm not transphobic, but... that's just such a strange choice. What's wrong with you that you'd want to put your character through that?" and things like that.
And I have also personally actually gotten flak OOCly from some people for my iRL sexuality when it comes up, because there are definitely not a shortage of people out there who don't think asexuality is actually a thing. "Oh, you just haven't met the right person; have you tried online dating?" "Oh, everyone loves sex. There's just something chemically wrong with your libido; you should look into medication to correct that!." "You're just afraid to try it; trust me, I promise you'd love it if you just gave it more of a chance." And so on. (Sadly, this is not remotely limited to online interactions.)
I'm sure many of them even think they're trying to help by basically going "Here, let me assure you that your sexuality isn't a real thing, and can even probably be cured!" Because, hey, they figure sex is awesome, right? But... try to envision telling a gay or lesbian person that their sexuality could be 'cured' by just sleeping with the opposite sex enough times, or with medication/chemicals. It's not a good look.
And when I played an asexual character on a game, I did have someone get OOCly mad at me that my character wasn't up to smash squishy bits even though he was not attached and thus 'up for grabs' and how that was 'unrealistic' that someone wouldn't want sex at all; that's the one incident that stands out in my mind about someone being terrible about my character's IC sexuality. (Bonus that it was one of the few times I've actually openly played my own sexuality as a character, so, y'know, great feeling there!)
So I've definitely observed people being terrible over someone's sexuality or gender identity, both secondhand and firsthand, regardless of whether it's IC or OOC. I like to think that's not nearly so widespread—or necessarily as deliberate—as it used to be, but yeah... there is still definitely some really awful behavior I've seen out there in the RP community in general to trip over.
...also this post was a little bit verbose and rambling, for which I apologize.