Mishandle (verb)

1. To handle something in a way that is not appropriate, skillful or careful.
2. To treat someone in a way that is not appropriate, skillful or careful.

Origin:

From mis- + handle.

Examples:

1. He mishandled the fragile vase and it broke.
2. She mishandled the situation and made it worse.
3. The company mishandled the customer complaints and lost their business.
4. The officer mishandled the arrest and was disciplined.
5. The manager mishandled the employee's complaints and created a hostile work environment.