I was the guest on an American radio show today -- SmartTalk on WITF in Harrisburg, Pennsylvania (see and listen here). The subject was clichés and people were ringing in and asking me the origin of a certain phrase, or just calling to say which particular clichés and buzzwords they hated. One common bugbear was the phrase 'my bad'. It means 'my mistake' and first came to prominence in the 1995 teen movie Clueless. One of today's callers mentioned the phrase 'my bad too' and that was used as the title of an episode of the medical sitcom Scrubs.
The phrase 'my bad' is not very common in Britain yet, as far as I know. But it is an example of a trend that is seen more and more often, namely where a word that was once an adjective (or a noun or another part of speech) is used like a noun (or a different part of speech). So, 'fun' was once just a noun, but now you will hear and see 'a fun thing', where 'fun' is used as an adjective. Other examples include 'will you friend me on Facebook?' and 'sex something up' (those two last phrases are examples of verbed nouns).