An example of the rhetorical trope of LITOTES (understatement), This is the delicate response one gives to someone who, in a group setting, suddenly blurts out information which is extremely personal, unusually revealing, and possibly unique to that individual. It comes from settings like group psychological counseling or 12-step groups, in which such highly personal testimonies are followed by the Moderator's cool "thanks for sharing." said smoothly-- no matter how disturbing or shocking or incredible was the confession that preceded it. This catchphrase may well have originated from the 1980's TV sitcom, BOB, which starred comedian Bon Newhart as a psychiatrist.
12-step member: "Hi, My name is Marcia."
Group: "Hi, Marcia."
Marcia: I just want to say I'm glad I'm here tonight, I'm a child of incest, I'm a heroin addict and I just murdered my husband"
Moderator: (Smiling benignly, completely calmly) Thanks for sharing, Marcia.