1. Spending time without purpose.
2. Getting involved with, interfering, manipulating or attempting to control another's emotional state of mind. Usually has a negative connotation.
3. One who is unqualified attempting to use, inspect, adjust, assemble, disassemble or generally fool or mess around with something or someone.
"What have you been up to?"
"Just jacking around."
"He has a reputation for jacking around with girls’ minds."
"I feel like you've just been jacking around with me."
"Don't be jacking around with your Dad's computer, or he'll have your ass when he gets home."
"My husband was jacking around with the plumbing to fix that dripping faucet, and now we can't flush the toilets if someone is doing laundry."