That one person for me would be this snot-nosed imbecile kid named Dara who was a few years younger than me when I was in my early teens. I used to be a hotshot skater kid (very egotistical) while Dara was a little imbecile with zero social awareness who could never catch a hint that I didn't want him in my presence. Just him being around me made me frustrated as I thought he degraded my social image by association. I sort of made him into the butt of my every joke since I viewed him as having less status than a chewed up piece of bubblegum glued to the bottom of my shoe. And no, I wasn't really a bully, he was just a little asshole who everyone rolled their eyes at. I even heard parents use him as an example of how not to raise a child. Even if you stripped away his abhorrent personality, he was just irritating to look at (literally looked liked that cringelord SammyClassicSonicFan when he was young). His hair that he never combed was usually disheveled and he sometimes wore glasses, plus his high-pitched voice sounded like nails on a chalkboard. It didn't help that he couldn't close his damn for more than two seconds either.
...As you can imagine, the thought of such a loser in my eyes fucking my mom would shatter absolutely every preconceived notion I could have and would be a fatal blow to my ego. I also love thinking of him having a huge uncut cock twice the size of my circumcised adult virgin penis and a limitless stamina, not to mention TERRIBLE hygiene and piss-poor behavioral skills.
One fantasy I enjoy in particular is of my mother perching Dara atop the throne of our household and treating him with an unreasonably high level of favoritism as if he was the son she never had despite him being an incompetent, good-for-nothing imbecile with absolutely zero gifts or talents outside of the bedroom, all while slowly worming me out of our traditional family dynamics as I find myself relegated to her irrelevant, seething, cuckold errand boy. Day after day of intoxicating, bed-busting sex causes her to become blind to his countless flaws and only see the best in him, while at the same time she looks at me with an overly critical eye, constantly pointing out my shortcomings and failures such as not fulfilling my duties as an ideal towel boy or condom-fetcher. My mom takes his side in arguments even when he is clearly wrong, and she doesn't even bother to listen to my logical and intelligent rebuttals. I feel my identity slowly erode which each passing moment as the little pipsqueak uses his massive penis to effortlessly manipulate her into granting him whatever he desires with the same ease as a toddler throwing a tantrum. I can only watch helplessly full of anger and jealousy on the sidelines as my sexy, ample-chested, blonde bombshell of a mother turns a blind eye to Dara's irresponsible behavior, even allowing him to start fucking her bareback without protection while I'm reduced to a desperate virgin pump-chump who can't even get laid in my mid-20s. I'd be called 'bonehead' and verbally chewed out as a 'useless moron' if I brought out her towel not warmed to just the right temperature for her to clean up her pussy after the morally bankrupt brat yet again finishes inside despite promising to pull out, but she doesn't even roll her eyes once at Dara's insolence as he fills her to the brim without even a slap on the wrist.
