You shouldn't delete things on your friend's phone.
Shawna has her friend Lacy's phone and is feeling mischievous.
Shawna wants to play a prank on Lacy.
Shawna takes pictures to put into Lacy's phone.
Shawna erases pictures that she finds on Lacy's phone.
Lacy will be amused because she can delete the pictures Shawna added.
Lacy will become upset because the pictures will be lost forever.