48. Yes, "my bad" is a proper English phrase. It is an apology; when you say "my bad", you're basically saying, "I admit a mistake" or "my fault, sorry for that". Wiktionary says: (colloquial) (idiomatic) My fault; mea culpa. Yes, I realize the humvee isn't supposed to be parked in the heirloom flowerbed. My bad. More @Wikipedia
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