Well, you ain't talking about me, I don't know Jack !!
( at least that's what my wife keeps telling me, but she does call me a jackleg mechanic at times )
Jackleg, adj., is a Southern adjective meaning inept, unprofessional, or dishonest.
It is usually applied to members of a particular occupation.
You do not, for example, want to take your car to a jackleg mechanic.
The term dates to 1837.
It may be from an older term, a jackleg knife or jackknife, perhaps first applied to carpenters who used jackleg knives.
Jackleg knife dates to 1786.