Yes, you can use your United credit for someone else.
No, you cannot use your mileage number for someone else.
No, it is not legal to use someone else's license plates.
Worldwide. Nowhere else
Screwdrivers all have a particular use and you really can not use something else to do the same job.
You can use the headphones for something else; or give them to someone else.
No, it is not safe or legal to let someone else use your credit card.
No, it is not legal to use someone else's credit card without their permission.
No, it is not permissible to use someone else's Square reader without their permission.
No, it is not permissible to use someone else's credit card without their permission.
in a threaten statement
You can use them for a poster, or something else.