A total, complete doofus who just can't seem to get anything right, ever. Can also be used to refer to an animal, such as a dog, who acts totally off-the-wall, unpredictable and sometimes anti-social.
That goddam black catahoula just went after my neighbor's friendly dog. She can be such a jack-a-leg sometimes.
by superaynumerouno July 13, 2009
Half assed or unprofessional. Not authorised or done while drunk. Someone who does a jack-leg job is called a jack
Look at that jack-leg job he did fixing the washing machine. The pipes aren't even screwed in all the way.
by Daniel b July 03, 2005
The Cooker: "Hey did you ever use Uncle Freddie as a lawyer?"
Pete Dick: "yeah, and he is a real jack leg, find somebody else!"
Pete Dick: "yeah, and he is a real jack leg, find somebody else!"
by Pete Dick July 05, 2008