Bob did something that Alice... doesn't really like. Anyway, she decides to just laugh it off, and Bob begins to laugh with her. Then before he realizes it, she plants her fist deep in his face, sticks a knife between his ribs, or pops a hole in him with a gun (her choice depends on her level of Ax-Crazy), with no trace of a smile on her face. They just had a moment of Pre-Violence Laughter.

Usually a case of Contagious Laughter, perhaps occurring before or during a Mexican Standoff, this is when two or more characters start laughing before one character draws a hidden gun or otherwise attacks the other character. In any case, one of two or more people goes from cheerily laughing, causing others to join in, to snapping out of it (quite possibly into anger) and doing something violent to indicate that they are getting dangerous. Going from laughter to serious violence always creates a