When did the term "my thing" as in "that is my thing" come into usage?
Merriam-Webster offers very little help and limits itself to saying
thing
7 a : something (such as an activity) that makes a strong appeal to the individual: forte, specialty
- letting students do their own thing —Newsweek
- I think travelling is very much a novelist's thing —Philip Larkin
and further on
10 : an action or interest especially that someone enjoys very much
- Music is my thing.
Best Answer
'My thing' as my métier, in 1841 and after
The 1841 reference to "do your thing" that Josh61 cites appears to be a reference to Ralph Waldo Emerson's essay "Self-Reliance," first published in 1841. Here is the relevant piece of that essay:
Why Ralph, you old hippie, you! Down with conformity; do your thing; tune in, turn on, drop out! I don't know whether Emerson's comment had any influence on the emergence of the phrase "do your thing" in the 1960s and 1970s, but a lot of young people read Emerson then (for school), and I was very pleasantly surprised to see how prescient his 1841 use of "do your thing" was.
To demonstrate that Emerson was not the only pre-1960s person to use "[one's] thing" in the sense of one's interest or area of activity, I offer this example from Daphne Du Maurier, I'll Never Be Young Again (1932) [combined snippets]:
'Your thing' as a proclivity or special interest, in the 1960s and 1970s music lyrics
There are actually two strains of meaning to "my thing"/"your thing" as used in the 1960s and 1970s. One is the laid-back, "following my own path" sense of the phrase, which finds expression in the Bob Dylan song "If Dogs Run Free," from his album New Morning (1970). Sample lyrics:
Isaac Hayes's "Do Your Thing" (1971) takes a a broad view of what your thing might be:
A 'thing' as an intimate relationship in 1960s and 1970s lyrics
In one sense, a thing could refer simply to an intimate relationship, as in Simon & Garfunkel's "We've Got a Groovy Thing Goin'" (from the duo's 1966 album Sounds of Silence):
Billy Paul's "Me and Mrs. Jones" (1972) is somewhat more forthright about the relationship there:
'My thing' as a source of sexual desire or jealousy in 1960s and 1970s lyrics
Somewhat suggestive of the same notion is the Isley Brothers' 1969 song "It's Your Thing," but here the thing isn't necessarily just a proclivity or a relationship but (suggestively) also corporeal:
That same year, Marva Whitney released a response song titled "It's My Thing (You Can't Tell Me Who to Sock It To), which puts considerable emphasize on the notion that possessing one's own thing leads as a matter of natural right to freedom of choice in the choice of a sockee.
In 1973 Sylvia Robinson included a song titled "My Thing" on her Pillow Talk album, where the phrase seems to refer either to her special relationship or to the person himself:
And in 1974, James Brown released "My Thang," which offers the following lyrical advice:
'My thing' as a source of sexual desire in 18th-century lyrics
Somewhat surprisingly, this last sense of "my thing" goes back to the English folk song tradition as the lyrics to "My Thing Is My Own" indicate. This is how the song begins:
This song appears in Henry Playford, Wit and Mirth: Or, Pills to Purge Melancholy; Being a Collection of the Best Merry Ballads and Songs Old and New, volume 4 (1719), and may it may be considerably older than that.
Conclusion
These examples—especially Emerson's from 1841 and Playford's from 1719—indicate that "my thing"/"your thing" has been around for centuries, with various colloquial meanings attached to it. The word thing invites both generalized and euphemistic usage, so it really isn't surprising that people have been taking advantage of those flexible features for a long time.