At the end of all the stealth missions during The Taiga level, you'll come to an old farm where you have to restore the generator in the building on your right as you approach and then restore power to the lift.
Once at the top (having taken the lift), you'll Come to a door that you have to kick open. Wait to be invited to sit down and do so. Drink the tea twice, and play guitar when it falls out the corpses hands. When he falls asleep and you get up the trophy should unlock.
A warning for curious players like myself
After the teaparty it still matters whag happens to the old man. The screen flashes white (earning karma points) for being kind to him. Shoot him dead, however, and the resulting negative karma pretty much wipes out anything you've built up so far, I actually think this is the most harshest of negative karma points in the game.