Trying to mess with a friend's car, how do I do this?

I'm in college and my best friend (also my roommate) has a girlfriend who thinks it's impossible for me to get mad so she told my friend she wants to mess with my truck to really try to piss me off. She wants to wrap it in saran wrap and put olive oil on that. My friend told me what she wanted to do cause he knows how pissed I'd get so we decided to mess with her car instead. I want to do this thing I saw on the internet a few months ago where you somehow tie her breaks in with her horn so every time she presses her breaks, her horn goes off. She drives a fairly new scion, so please help me figure out how to do this!