Whoa, that is completely out of order. You need to let them know in no uncertain terms that you do not give permission for this person to handle them! I'm sure you already have but can you get your parents involved or something?
They might just be teasing you but I can only imagine how miserable you'd be worrying about this while you're away, you need to ask them to be serious for just a minute
I have an uncle who would tease me all the time and when I was younger he would just keep at it until I got really upset, he didn't know when to just stop and leave it so maybe I'm projecting a bit here...