I've only ever heard people say "my bad." Never heard anyone say "my bag."

my bad: Etymology: Seems to have originated from a phase by Manute Bol, A player of Sudanese origin for the Golden State Warriors basket ball team in California. Other players picked it up and started using it. (colloquial) My fault. "Yes, I realize the humvee isn't supposed to be parked in the heirloom flowerbed. My bad." http://en.wiktionary.org/wiki/My_bad Used to acknowledge that one is at fault http://www.thefreedictionary.com/my+bad "My bad," an exclamation meaning "my fault" or "my mistake," evidently arose in the mid-1980's among players (primarily Black) in informal "pick-up" basketball games. One player would throw a bad pass or flub an easy shot and say "My bad" as a sort of handy shorthand for a more elaborate apology. The term's transition to more general slang use was apparently greatly accelerated by its inclusion in the enormously popular film "Clueless" a few years ago. As to "my bag," it's been slang for "personal style or preference" since the early 1960's, but I've never heard it used to mean "my fault." And "my bag," which comes from the slang of jazz musicians, is unrelated to "holding the bag," which dates all the way back to the 18th century. http://www.word-detective.com/121597.html#mybad

It's "my bad"....I HATE when people say that. I think it sounds incredibly stupid.

my bad...but I hate it. It's not English.

'My bad'. I think it derived from a gang slang.

It's "my bad"--that poor excuse for saying "Sorry, I've messed up. But I'm too lazy to put my words into plain English."

Well, since usage is really what matters, "My Bad" will tin out since it is now what stands as the expression. BUT.. I can personally account for the use of "My Bag" being used fairly extensively back in late 80's early 90's. I remember thinking then that it was used as a reference to "I am left holding the bag" which is an expression used to imply one is at fault for something. Therefore, "My bag" was used. I believe you may be able to find a movie in that era that used "My Bag" in the script as I think I recall hearing it on a major motion picture. But I can't recall which movie it was.

My wife and I have this argument all the time. YES in the mid 80's to early 90's it was MY BAG as yes my fault or used to denote fault. I am 44 and my wife is 33. She claimed it was never my bag but she is wrong. I am so thankful other people my age remember. If you are under 40 you probably have never heard that expression before.

That depends on the context. Use "my bad" when you are accepting responsibility for an unhappy or unsuccessful outcome. "My bag", on the other hand, can mean "an activity that you like or at which you are superior".