My cousin is a complete creep :S help!?

Hellooo, ok so I'm 15 (turning 16 in a month) and im pretty and all, if that makes a diference, and i have this cousin thats soo creepy. Hes 18 and like, idk he makes wierd faces and noises, he's lke really insecure to talk or idk.. but still sometimes he just stands next to me when im using the computer and stares at me and i say.. yeah?? and he says,,''oh no, nothing''! its so wierddddddddd! and like whenever im using the computer he'll just go up to me and ''scare me'' but grabbing my shoulders and saying like ''boo!'' but its so lame and it just makes him creepier! like idkkk I'm like scared of him!!! yesterday we had to walk down this dark road together and i swear i was just about to run away!! ughh help!!! hes living with us for like 3 months cuz hes studying in my area for the moment but really help! i dont know who to tell or what to do! he gets creepier every time!! i dotn want anything ''bad'' to happen! :S