An expression used to denote an extreme bummer of a situation. Origin: portmanteaux of "scrumdiddlyumptious" (word coined by Roald Dahl in his book "Charlie and the Chocolate Factory) and "bummer."
Matt: My parents ate all of the seafood pie I cooked! There's no food left for me-- and I cooked enough for 8!
Ned: Aw, that's bumdiddlyumptious!