@alipz fairly sure those two words are synonymous to suicide, and that everyone still frown upon it. The former is a waste (hey, TIL that japanese is the only language with a word for "waste" (obviously! lul lul). Watched "japan sinks"... its bad) and the latter is both a waste and less a suicide and more a suicide attack.
I think you wanted to say 'Sudoku'. That is the thing that noone frowns upon
But yes, the end is left open. personally I like the interpretation that the guy gives up on taking his life because of the receipt. But it is never shown if he changes his mind or not.