Really? I think I know a combination of both of these when starting my most recent story "Rigamarole" and I don't usually have a hard time figuring out things my OCs dislike and why.
For instance, my male lead in "Damsel in the Red Dress" dislikes messes, chaos, anytime anything is out of his control. That's because he was raised to be perfect, his mother is the pinnacle of perfection, and he tries with everything in him to be as like her as he can be so she'll be happy with him. My female lead doesn't like roses. This is because they remind her of her ex-boyfriend, who once had her do a photo shoot for him called "bed of roses" which is now a pretty traumatic memory for her, and because her mother was obsessed with roses, and she can only associate her mother with nightmares now. (her mother's name literally was Rosa, which I only realized at this moment, but Alicia (female lead) has had a strong aversion to roses since the first book.)
I usually know a lot of their likes as well, and though those don't always have to have meanings behind them, they occasionally do.
The male lead likes cats because he feels like he has a connection to them. He received his name "Kattar" because his mother thought he looked like a little black cat when he was born (because of his eyes and the fact that he was born with a full head of black hair.) He's also a big fan of driving and traveling alone, because these things always made him feel independent of the stress he lived with daily.
The Alicia lead is very affectionate and loves Xs and Os, there doesn't technically have to be a reason for this, but it's always both been her love language and something she found comforting (Though trauma now makes that a mixed bag.)
In "Rigamarole" the male lead dislikes people chewing loudly. Might seem irrelevant, but he is bulimic, and even being reminded of food is triggering to him. The female lead values her privacy and dislikes people who don't knock, or don't respect her privacy. This is easy to understand for me, because every time people have discovered her secrets in the past, her life became living hell and virtually all her privacy was stripped from her (full-on, her parents removed her bedroom door.) She hates anytime people treat people like they are less than others because they do things people disagree with because she's so used to feeling less than human or like she can never be treated like a "normal" person again because of her struggles.
She and her brother both like riding bikes because it gives them a sense of freedom. She loves books for the same reason because they allow her to think about something other than her life for a little while.