I'm currently reading "The Opposite of Fate: Memories of a Writing Life" by Amy Tan. Her mother took the cake for pessimism. Some of the choice wisdom she passed on to her daughter (as quoted by Tan, Chinese inflection and all):

Her Mother's version of "Look both ways before crossing the street:" "YOU DON'T LOOK YOU GET SMASH FLAT LIKE SAND DAB."

Sex education: "DON'T EVER LET BOY KISS YOU. YOU DO, YOU CAN'T STOP. THEN YOU HAVE BABY. YOU PUT BABY IN GARBAGE CAN. POLICE FIND YOU, PUT YOU IN JAIL, THEN YOU LIFE OVER, BETTER JUST KILL YOURSELF."

When her father caught a rat in a trap: '''SEE,' my mother had soothed, 'NOW YOU NO LONGER BE SCARED WHAT WILL EAT YOU.'"

When a playmate died of cancer: "THIS WHAT HAPPEN WHEN YOU DON'T LISTEN TO MOTHER."