Opps has 2 p's. My bad is usually used by teens and it is slang that will probably be out of use within the year. Also if you embarrassed someone, it would be treating the situation too lightly if you said, "My bad". For the example sentence that was given above, We would say, " We were out of meat, drinks, and Guarana for the kids." You couldn't use weren't if you have meat after it. Because you used drinks after that, the whole sentence is awkward and that is why I changed it. Also, the expression is an apology for embarrassing someone or for having caused someone embarrassment . The expression means what Donay said. Good try, though!