Little sister syndrome, or the syndrome that affect people who always want to be included or to know what's going on, even when they don't understand. People with this disease love to hang around older people, even when they are not wanted. (They do not have to be literally a little sister.) Also can affect males, but it is especially insulting if attributed to them.
I must have been so annoying with my ls syndrome when I was younger. I remember I begged to go to the mall with my big sister and her friends, and then I dragged them all to the Hello Kitty store. God!
When Jenny liked that one councilor, she developed major ls syndrome. She stayed with him all day at the boardwalk, and started laughing at jokes she didn't even understand. It was so embarrassing.