Wanna scare the shit out of a slutty friend or promiscuous enemy?
Send them an anonymous STD notification letter and wait for the hilarious action to unfold.
The letter will inform them that you're a past sexual partner of theirs and have recently been diagnosed with a serious, sexually-transmitted disease.. and you were required by law to report it to them.
You pick the STD!
For added authenticity, the letter will be personalized with their first name.
Just imagine the countless hours of panic and worry they'll endure before getting themselves tested and receiving the results. It could take weeks before they know something!
And who knows? Maybe they really will have a disease. Either way, it's a win-win. For you, that is.