EVERYONE Has Read This but Me - The Catch-Up Book Club discussion

Mm, fun question. Depending on whom I'm recommending it to, I'd say To Kill a Mockingbird or
The Importance of Being Earnest (a play, but still). Also, perhaps Anne of Green Gables or The Lion, the Witch and the Wardrobe (not because I necessarily think it's that good, but it's very short and a fairly inspiring plot). Oh! Also The Haunting of Hill House for anyone into more haunted-type tales.

The Picture of Dorian Gray by Oscar Wilde
Rebecca by Daphne du Maurier
Frankenstein by Mary Wollstonecraft Shelley

This comes from someone who grew up on somewhat different set of classics (and tends to have unpopular opinions about most of the required )

For those who need them still relevant
The Master and Margarita - I was close to putting it under "for everybody", but I don't really think there are books for everybody.
Animal Farm - with the caveat: rather then trying to guess what time and place it is about, focusing on the link between changes pushed and language used to describe the changes.
Honorable mention: Limes inferior - I guess it's time to stop hoping someone will translate it and get down to it myself.

For those who want fun adventures
It's hard for me to put something here, because in my country adventure classic starter pack are Kornel Makuszyński Alfred Szklarski and Karl May
I've always liked James Oliver Curwood much more than Jack London too.
A Connecticut Yankee in King Artur's Court - could be a gateway to both Utopia genre and Arthuriana.
With Fire and Sword - for those who already read and liked some modern historical fiction.
The Name of the Rose - for the crime readers.

For horror fans
The Monk - for those who feel the need to see every film with a scary nun in it (is it filled to the brim with the most annoying horror tropes? yes. is it so horrifying you can forget all about it while reading? also yes).
In a Glass Darkly - for those who will complain about every plot hole but will keep on watching/reading horrors anyway.
The King in Yellow - another one I was tempted to label 'for everyone'.

More realistic drama
The Forsythe Saga
The Blue Castle
Sense and Sensibility
The Sorrows of Young Werther
Three Comrades
anything by Nikolai Gogol

Less realistic drama
The Street of Crocodiles
The House of the Spirits
I suppose Hermann Hesse fits here. I'm not a fan but he was always hugely popular among my friends. "Demian" was a relatively painless read.
Honorable mention: One Hundred Years of Solitude - a book that got me out of the longest reading slump in my life. However, reading the reviews on Goodreads makes me think the English translation must have lost the very things that worked miracles on me, so I can't really recommend it anyone who will read it in English.

Oscar Wilde

I agree, needs to be easy language, relatively short, not much description and an active plot throughout to keep them hooked (as they'll be biased to think its 'boring') so needs something that won't be.

I'd say Pride and Prejudice (better if they know the film) or Persuasion are a good shout.

Wuthering Heights I think shows how classics can be really dramatic.

Dracula is also a fun one, especially with the emails for it in 'real-time' & the memes.

Finally I think an Agatha Christie is a good shout.

Ali wrote: "This comes from someone who grew up on somewhat different set of classics (and tends to have unpopular opinions about most of the required )..."

Your list is awesome. I have added many books to my Wish List today. Thank you!