For ending 0 you just have to go to the toilet and do your thing. When your neighbor asks for some toilet paper, leave the stall and go through the door.

For this ending you just have to interact (F) with the hand dryer 2 times and that should kill you and give you the ending.

For ending 2 you have to grab the grenade from the vent by opening it with the screwdriver (the screwdriver spawns on top of the hand dryer after you get ending 1 and 7 (i think))or giving your neighbor some toilet paper. Now you just have to pull the pin while holding the grenade and let it kill you. BOOM! Another ending.
(I dont exactly know the conditions for the screwdriver spawn so if it isnt there just continue doing the other ending until it is there)

For this ending you have to grab the grenade again and pull the pin. Put it on your toilet and you get another ending.

For this ending you also need the grenade again. Knock on your neighbors door and then when he reaches his hand out under the stall pull the pin and give it to him. Another ending.

For this ending you have to kill yourself with the grenade again, but this time pull the pin and drop it on the ground and stand on it.

For this ending you have to peek into your neighbors stall. Just jump while hugging the stall and you should get a warning that you can't peek in other stalls. Click on I can't be stopped and let the tentacle kill you.

After you get ending #1 the hand dryer should be fixed. Interact with it again for ending 7.

For ending #8 you have to grab the axe by exploding the door (or where the door was) with the grenade, walk through the black part and grab the axe. Now chop down the stall with the yellow door that is next to your neighbors stall and grab the gnome. And then right click while holding it for the ending.

For this ending you just have to throw alot of items into your neighbors stall (sodas gnome papers) until you get the ending.

For this ending you have to go outside the toilets by exploding the door and just walk over the banana peel.

For this ending you have to explode the door again. Then go to the door with the code and put this code in:
Blue 2
Orange 6
Pink 5
Green 9
Yellow 1
Red 8

Then you just have to walk through the door and wait for the ending to be given.

For this ending you have to open the door for ending #11 again and this time bring the gnome with you. This should give you the final ending of the game.

For this achievement you just have to grab a paper out of the trash that has a character on it and says 'i belong in the trash' then you just have to go to the urinal that is left of the rightmost urinal, grab the poster above that urinal and throw it into the trash for the achievement.

For this achievement you have to interact with the door that you came in from when you enter, just spam F on it so that it sounds like the beat from "we will rock you". Eventually you will start singing the song, continue until you get the achievement.

For this achievement you have to get the grenade inside the vent first (mentioned earlier how to get) and then peek into your neighbors stall and choose "I can't be stopped" (also mentioned earlier). Pull the pin of the grenade and throw it at the tentacle to kill it and get the achievement.

Congratulations! You now have fully completed the game. I will try to update this guide if the new dlc releases.

Thank you for reading my guide and have a nice day.