Barnacle (slang)

"Barnacle" is a word people use as slang to describe someone who won't leave you alone. Imagine you are playing with your toys and a little friend comes over to play with you. But this friend doesn't want to stop playing with you even when you get tired or need a break. They just stick to you like a barnacle sticks to a rock in the ocean. That's what it means when someone is called a "barnacle". They are just always around and won't give you space.