This is unlike most games in that you'll need to start and run many separate 'playthroughs' (parties) in order to get the achievements - with a different strategy and outcome for each. So, technically all the achievements are missable/soft-missable - but given its (deliberately) a game of many iterations over a short 'story' they're all marked Optional.
Note that often the Steam achievement won't unlock while you're in-game; only when you exit. You should get in-game achievement popups at the right time though...
Difficulty does NOT affect achievements
No missable achievements (plus 16 unknown)
Sign in with Steam or Xbox to track your progress, and:
Complete Katherine's story and help her get back at her boyfriend
Sweet talk your way into unlocking Madison's special social abilty
Get caught by another character in the middle of some sexy time!
There's plenty of ways to do this, but maybe the easiest ways are either (a) go down on Stephanie in the family room, or (b) have sex with Vickie in the pool
Politely listen to all of Patrick's epic back-story.
Get Vickie Vixen to show up at the party.
Meet all of the characters at the party in one playthrough
Show off your artistic skills and ruin a friendship to get a reward from Madison!
Thow a dildo at it. Obviously. Do we have to tell you everything?
Help Stephanie discover her true calling in life.
Complete Amy's story and win her affection
Complete Rachael's story and win her affection
Inspect at least 30 items in one play-through.
Outside of "Derek Smash!", get Patrick beaten up 5 times in one playthrough.
Complete Ashley's story and help her prank her sister!
Take the high road by not sleeping with Madison and experience the wonders of friendship with Derek.
Complete Vickie's story for a "hot" ending.
Yeah I mean...you can, but why would you?
Avoid Frank’s AND Derek’s fists for at least a minute.
Get Ashley drunk and get her to start some trouble!
See what Stephanie REALLY thinks of her boss by completing her DnD.
Complete Amy's Scavenger Hunt path
Smooth talk your way to Ashley's affection without completing her story-line.
Give Frank a concussion, then take advantage of the situation and free the booze!
Complete the Opportunity "Viva La Lety".
Strip at the door, make your first impression to everyone in the nude
per description; strip at the door right at the beginning of the game - then walk up to each of the people to get a reaction from them.
Use the checklist below - but remember this has to all be done in the same game/party:
Sign in to track your progress against these checklist items
Give Patrick Rachael's "Death Mix", and do what it takes to shut down his site!
Experience a better life through chemistry, and shed six pounds at the same time! Thanks Laxapas!
Give Madison a few and see what happens when she takes on the persona of her favorite reality TV star.
They're smarter than they look! Experience the Easter Egg ending of Lety's content.
Experience a magical, non-violent, artistic moment with Frank.
Get to the bottom of Patrick and Rachael's drama, and help Pat win her over!
Unlock Compubrah, learn about Patrick's businesses, and maybe, just maybe, stop a Skynet situation from playing out.
Reverse pickpocket an item into Patrick's pants during "Disrupt the Disruptor".
Get on the "sh*t list" of every girl at the party.
You have to be rude/horrible to every girl - except Vickie Vixen who doesn't count.
Help Leah bring the serpent to a swift end, and reap the rewards...
Provide a little inspiration, a bit of fitness guidance, and a nutritional treat to increase Leah's power level.
Stoke the fires of rivalry within Brittney by giving her an extremely fishy gift.
Watch the Game Grumps cause a scene 8 times in one playthrough. Don't forget to subscribe, thumbs up, rate me, updoot, etc...
Peg Frank with a sex toy while he is dancing on the roof. Not peg...hit. You get it.
Convince Leah to abandon her lawful ways...and survive!
Defeat Frank 1 on 1 without any sparring or combat training.
Successfully interrupt Leah and Lety's conversation with a popper, from very long range.
Reach a... climactic moment with four ladies in one playthrough.
Do the opposite of this, and get onto their noble steed! Yeehaw, and stuff.
Punch Frank, Derek, and Patrick when they're not looking and not in combat, all in one playthrough.
Help the Game Grumps leave the party using the magic of virtual reality!
Get Frank to join the D-Club.
Reach a... climactic moment with two men in one playthrough.