Awkward/tricky/tough etc customer noun
Used to refer to a person who is difficult to deal with
This morning Nick helped me deal with a tough customer.
You should use the tough treatment for these tricky customers.
Someone who has a strong personality
It is difficult for someone (not) to do something.
To be difficult, troublesome, or unpleasant for someone; to be to someone's disadvantage.
Used to describe the action of treating someone very strictly.
If you say that someone or something is too hot to handle, you mean that they are too difficult or dangerous to cope with.
It was often said by a photographer when he would like small children to look at the camera and smile before he took a photo.
When the photographer said “watch the birdie”, all of us looked at the camera and smiled.