I'm quite notorious for scaring people and making pranks. I think the best one involved the girl from The Ring films (you know, the girl with the nightdress and long black hair...)
It started with my housemate and I constructing our own Ring Girl from a white sheet, nightdress and long black wig (I have one as I dressed as her for a party) around some small step ladders. We left her in other housemates rooms, which scared them lots when they saw her behind their beds or something when they first went into their rooms.
We kept moving Ring Girl around the house for the next week. Eventually our other housemates were all "We're used to her now, she doesn't scare us!" Which was perfect, because...
...one night the housemates went out. Another friend in on the joke texted us when they were coming back. So I, yes, I! donned the white night dress and wig and knelt on the landing, just around the corner from the top of the stairs. I looked EXACTLY like the Ring Girl model we'd made. Housemates come upstairs, turn the corner, see me. "Haha, very funny, we're not scared anymore". That's when I lunged at them. I've never heard people scream so loud. Brilliant.