1) Put a sharp weapon in your pocket (Preferably a knife)
2) Tell him to follow you to the bathroom
3) When both of you are in the bathroom, stab him in the heart.
4) Position him on the toilet, lock the door, and cover up the blood with paper towel or toilet paper.
5) Flush the paper towel / Toilet paper down the toilet once done cleaning up the mess.
6) Tell no one about it. Forget it.
Done.