What's a better way to scare someone?
Hiding in wait at someone's front door of their home, or at the front door of a store?
Dress up as slenderman! ;D
Their home, especially late at night. If you do it at a store they wouldn't be as scared, seeing as they are expecting people to be there.
i say hiding in their bathroom :p
<--------- dress like that and play the song HAHAHAHAHA by Twiztid and you might scare em easily.
Put on a scary mask and when someone walks through the door give em a good scare.
My favorite is to sneak up to their bed, and play a REALLY REALLY loud song, as Loud as It goes, in the middl rig the night. I recommend you run, they won't be happy :)