I heard this quite a few times in HS......
-Freshman year(ninth grade) I was told I looked(and apparently dressed) like one, by my alleged "friends" of all people: This was how it started, firstly by this alleged group of "friends," which then others picked-up on, due to a mix of word of mouth & people just deciding I was deserving of that title. It didn't help that at the time, I had a thing for wearing very black clothes, which ofc gave them more ammunition.
-Later that year, I heard of a rumor that someone(Idk who, they may have been older) took a picture of me one day of me & wrote some meme caption on it about how I was a "school shooter" on Shitchat
-Sophomore year(10th grade) I overhear two foids in class talking to each other in their obnoxious "teehee" sounding voices, talking about people in our class: Eventually, I get mentioned & immediately one of them says "
: OMG that DarkStar kid looks like a school shooter teehee" which caused both of them to giggle as hard as they could for a few minutes.
-Junior year(11th grade) I see an acquaintance in the hallway I thought I was cool with, I say "hi" to him in a friendly tone, and he just smirks at me & says "hey school shooter"
-Another point in that year, an acquaintance mentioned to me how he overheard some kids, I think it was a group connected to the acquaintance mentioned above, joking about me being "most likely to shoot-up the school"
-Senior year, I was in an art class, and these kids who were younger than me(I forgot which specific grade) were joking around: I caught them glancing at me, and then vaguely overheard them saying "doesn't he look like a school shooter?"
Keep in mind, one of the earliest "Incel" caricatures/stereotypes is the scrawny, quiet, nerdy, weird White kid who everyone joked about & mocked in some way: This also likely is an Americancel/Burgercel trait, due to the stereotype of shootings occurring here.