If you've ever watched The Crow as a sober adult, it's hard not to laugh a bit at Brandon Lee's performance in that movie... That's not to say he couldn't have been a big star, but his acting ability left something to be desired.

Unrelated to Lee (but related to the topic), one of my all-time fave films is a Russian drama called Vozvrashcheniye (or The Return) about two young brothers whose disturbed father returns after many years and takes them on a trip. In an early scene in the movie, the boys are cliff-jumping into a lake; very soon after the completion of filming, one of the two young actors actually drowned in the same lake...