How do you have two Sims to have "awful compatibility" ?

Have one of them dislike small talk and have the other enjoy it and choose this interaction constantly. That's worked well for me . 

Basically you could have one dislike any type of interaction and have the other like it and continue to do it.

You need to add something they dislike in the other sim. Like say they dislike pink and the other sim has pink hair or clothes or nails. Or one likes boho clothes and the other likes preppy clothes. Also conflicting traits, one nosey, and the other one is paranoid, or cheerful and gloomy. 

I usually try to accomplish good compatibility by giving them matching likes for conversation topics and have them like sim characteristics that the other sim has. So I think you should mismatch conversation topics, have one sim like gossip and the other sim hate it. Or have them dislike each other's traits. For example if one sim has the  loves the out doors trait then give the other one a dislike for nature enthusiasts.

Quick test. I created two sims

Sim 1 sceptic, nerd and childish 

Sim 2 snob, high maintenance and art lover

Test 1

• Sim 1: dislike artsy sims
• Sim 2: dislike intellectual sim
• Result: bad compatibility 

Test 2

• Sim 1: dislike artsy sims 
  
  Sim 2: dislike intellectual sim
• Add opposites on conversation topics deep thoughts, small talk and stories 
• Result: bad compatibility 

Test 3

• I tried to add more dislikes and mismatched conversation topics. Even had one sim hate colours and music loved by the other sim but wasn't able to get awful compatibility in my quick test.

I have seen awful compatibility in my game but usually try to avoid it. Getting awful compatibility on purpose seems more difficult than I thought.

I think you best look at this list by EgonVM​  to get more information. It includes how much each trait weighs and you need to get to - 6 or lower for awful compatibility. 

https://forums.ea.com/discussions/the-sims-4-general-discussion-en/compatibility--self-discovery-explained/5002975/replies/5003198

If you hold the mouse over the various sim characteristics in the Likes/dislikes panel,, it will tell you what traits (and it's traits, more than other areas that will impact compatability) affect compatability.  In my save for the Event, All members of the family have the Adventurous trait, and also like sims that have similar traits (I want to say Spirited and Nature Lover, but double check) because I wanted a very close knit family for that save.
If I'd wanted to say make the youngest isolated, I could have given her the Creative trait, and had all the rest of the family dislike Artsty sims.

really?  🤣🤣🤣🤣There is soooooooooo much to choose from! How can this be difficult?  My game makes all my sims be mean to each other all the time!!!!  🤣🤣🤣🤣  I literally do not even need to try!   🤣🤣🤣🤣Can we trade????   

rujuta4me​ Yes please! 🤣 I want my two Sims to hate each other! I honestly tried! 🤣 We can trade. Let me know when! 😇😅

True. I will look at the traits that aren't compatible. Thank you! But I honestly thought that dislikes/likes would do it.

Thank you for testing! And thank you for the link! 

I did make one Sim like art the other Sim dislike art. I added other things like favorite color is purple and made the other Sim dislike purple.  Just didn't work. It didn't even give them "Bad Compatibility"! 😩

I shall take a look at EgonVM's thread. 

I did try this with the hair but I realize I use CC and the hair might not be categorize as the color. I mean Sim 1 dislikes blue, and I gave Sim 2 blue hair. I also made Sim 2 favorite color blue. Again, it didn't even give them Bad Compatibility. 😭I will try it with the clothes though. Thank you!

Thank you for replying! I did this honestly. One Sim likes compliments and the other hates it, nothing changed. I tried giving them opposites in everything basically.