One way for me: watching a Bobshauex review. I was watching Bob review the RL Stine made-for-TV movie "When Good Ghouls Go Bad" and at first I was like "oh huh wonder why I never heard of this before." Then I get to the part of the review where he shows the scene where Christopher Lloyd's character ("Uncle Fred") is killed by a mountain of pumpkins falling on him (that sentence makes sense in the context of the movie), suddenly I had a moment of "wait! I've seen this movie!" Not only did I remember seeing this movie a long time ago, but I remember that on the day I saw it I had rented Mario Tennis for the N64 and played that most of the day. I think the reason why that scene alone caused me to suddenly remember is because something about that death scene bugged me as a kid, and part of the memory of that day kinda just lingered in the back of my mind.
Another one that happened a while back was when I was searching deviantArt for the "usual" stuff I look up, and came across artwork someone did that was based on an old episode of All That. That's when I suddenly remembered, there was an old episode of All That (original cast) where, in an Oprah parody, there was a scene where some girl demonstrated a special talent of drinking a ton of tomato juice. The art was directly based off that scene, and even included a link to the episode in question. After rewatching it I was like "oh wow that scene was darker than I remembered…" as the scene ends with the girl "popping" off camera and the audience being sprayed in "tomato juice." Yes it kinda looks like blood, and I just went "even for the 90s, I'm surprised Nickelodeon actually got away with this."