Yes I decided to make a guide for F2P Source Mod almost ten years after people stopped playing.

It's pretty easy.

1: save in the bedroom
2: go down the basement, through the hole in the floor of the showers.
3: Once you're in front the door where you use the old key to open it, open the console (should be "p" on your keyboard, change in settings if neccessary), type in "sv_cheats 1" and press enter
4: then type "ai_disable", copy it but DO NOT press Enter yet.
5: go through the door.
6: choose the 2nd dialogue option.
7: The 2 men will attack and you'll have to open the console and paste the command from before and press enter, those guys can kill you in a few seconds.
8: The'll just stand there, menacingly, and you're free to shoot them. Just kill one of 'em and the achievement should pop up.

The chance that anyone will see this guide is extremely slim nowadays, but if you somehow stumble upon it, feel free to leave a comment.

Also, this is my first ever guide so congrats to me i guess.