Having a habit of stealing or being light-fingered; someone who tends to take or touch others' things without permission.
あの人は手癖が悪いから、荷物から目を離さないで。
That person has a habit of stealing, so don't take your eyes off your bag.
彼は子どもの頃から手癖が悪く、よく家の物がなくなった。
He had a habit of taking things since childhood; things at home often went missing.
手癖が悪いと噂されているが、証拠がないので注意して見ている。
He's rumored to be light-fingered, but with no proof we're watching him carefully.