The last two mornings Susan had a little meltdown as she left the house for work. Neither was created in a vacuum, the husband's mouth was present.
Yesterday's explosion was immediate, and it only took a little nudge. Today's was just as quick and ended with Susan throwing a banana.
In each case the cause of the argument wasn't really significant except for the one where the husband started a conversation then lost interest when it was Susan's turn to talk.