Must've been around 13-15, went to a pizza hut with my then girlfriend. I saw a darker skinner, heavy-set lady walking over to the counter with her two kids, all of them looking a little dishevelled. Without thinking I said "She looks poor" in probably a demeaning manner to my girlfriend, and she answered "you say that like it's her fault".
I'm dumb as fuck so the penny didn't drop until several years later about the reality of my privilege, and how unfair and fucked up the system really is. Nearly ended up alt-right, now I'm a comrade.