Should've knocked off work, jumped into your car and followed him home. Three weeks later sneak into his house during the dark, chilly hours of the morning. Put your handkerchief (dribbled with chloroform) over his mouth and nose to ensure he doesn't wake up. Tie his arms and legs to the bed. Strip him naked. Install a mirror over the bed. Cover his body with fake blood (1 part water, 3 parts corn syrup and food dye). Now the tricky bit. Take his nob and tuck it in under his arse and tape it up tightly(he is knocked out he won't wake and make sure you hide the tape with the fake blood). Install a tiny remote sending camera that will send his awakening to your phone, make sure it is very well hidden. Now sneak out of the house. If all has gone to plan, when he wakes up his nob will have pins and needles and feel completely not normal. As he opens his eyes and groggily looks he will see himself covered in blood. With the extremely weird feeling down below his eyes will immediately search the mirror for that area and find his penis missing, the area covered in blood and his arse will hurt (the tape pulling at his arse hairs). Enjoy the horror you have created and laugh quietly to yourself as you drive away to his screams for help.