It depends what they did; a letter from the state attorney general's office, which is usually the (US) state's Consumer Protection Office, works. I shut a bank's VP up with letters from a lot of people--who all received identical letters from. Have it well-written, though. False info = felony.
Links to videos where faces pop up in the middle of the video and a loud scream occurs. Tapping on their window softly in the middle of the night. Be careful that they aren't packing heat if you go for the latter, however.
well i like fake blood just pick a good time and when you know that person is going to come over then you mess up the house like someone broke in then lay on the floor with a lot of fake blood on the floor and all over you so they think you are hurt bad
The best time to scare someone is when they are sleeping; be sure to wait long enough that they forget you owe them a scare. There is the classic air horn, but a more fun scare involves silently lifting the covers and pouring fake blood (realistic looking) all over their stomach, then wake them. Fun.