Another thorn in my side is when people refer to other people as 'that'. I can't believe how many times I hear someone talking about a person or group of people as 'that'. So here is the simple rule:

"Who" refers to people.

"That" refers to things.

Examples: "The lady that put the pie in the window was enticing me to steal it."   

or - 

"There were so many people that didn't know how to ride a bike."

These should read:

"The lady who put the pie in the window...."

and - 

"There were so many people who didn't know..."

These are correct uses of that - 

"The house that was made of stone was built in 1850."

"The boy knocked the radio, that was set on the table, onto the floor."

Some people refer to animals as 'that'. I never do - they are living, breathing creatures and as far as I'm concerned are considered 'who' when talking about them in a sentence.

Example: 

"Kitsu is a dog who loves a good bone treat."

My dogs are family members and are loved and cared for as I would care for any other family member. Therefore, to me, they are referred to as 'who'. Some may disagree but I would be correct. This is a personal choice.