"I may have thrown it away. I don’t remember."
Do you really not remember or were you trying to get rid of something you didn’t want in the house? Be honest. Throwing away that prized leather ball, the too-tight college shirt, the tired old coat might have been on purpose but you anticipated a negative reaction. Better to say, “I did throw it away. Are you upset?” And better yet, “I want to throw this away, is that OK?”