An exclamation used equally in times of excitement and frustration, designed to cause a similar feeling in the one to whom it has been said, yet utterly failing to do so. Originally used in Jane Austen's 'Pride and Prejudice'
1) Anger: ie, upon finding out your husband has just told your daughter he will never speak to her again should she marry someone you feel is a suitable match: "Oh, Mr BENNET!"
2) Delight: ie, upon finding your daughter is going to marry one of the most eligible men in the country, although he may own the miserable half of Derbyshire: "Oh, Mr BENNET!"
Other exclamations are also acceptable.