I have two, actually. Not sure if they're from the same movie or not. The first one involves a woman standing on a ladder which is in the hallway on the second floor, by the balcony. Someone (perhaps a child) pushes her off the ladder and she goes flying over the railing and hits the ground and dies. I thought that perhaps it was the scene in THE OMEN but it isn't. This is from a different movie.
The second trauma I have involves a birthday cake. I don't remember if it was a woman or a child, but just before or right after they blow the candles out, some sort of creature pops up from the cake and lets out some sort of ghastly scream. For a long time I was leery of birthday cakes because of this scene. Hope you can help!
UPDATE: The "Bad Birthday" trauma stems from the 1983 PETER WELLER classic OF UNKNOWN ORIGIN. Special thanks to reader jaakko, and check the comments for a clip.