Sims randomly fighting?

@GnatSexy I found several possible reasons that you could check to see if they match your situation:

• A spell ("The Curse of Unwarranted Hostility"): https://answers.ea.com/t5/General-Discussion-Feedback/Sim-keeps-Fighting/m-p/8268604#M16629
• A NAP ('Roughhousing Encouraged'): 
  https://answers.ea.com/t5/General-Discussion-Feedback/Constant-Fighting-at-Restaurant/m-p/9180199#M30240
  https://answers.ea.com/t5/General-Discussion-Feedback/Constant-Fighting-at-Owned-Business/m-p/9723357/highlight/true#M39526
• Restaurant visitors fighting: https://answers.ea.com/t5/General-Discussion-Feedback/Restaurant-visitors-keep-fighting/m-p/9288769/highlight/true#M33104
• Frequent fights and other issues (also NAPs): 
  https://answers.ea.com/t5/General-Discussion-Feedback/Sims-steal-drop-actions-random-romance-etc/m-p/9208506/highlight/true#M31054
• Fighting on community lots: https://answers.ea.com/t5/General-Discussion-Feedback/Fights-amp-Baking/m-p/9471261/highlight/true#M36638
• Sims with personality traits that are particularly difficult (evil, etc.)
• Is it 'Neighborhood Brawl Day'?
• Do you play with Mods or CC? If you do now or have in the past, you could test if that's causing the issue (click spoiler tag):
  
  Spoiler

  Move your Mods folder from your "The Sims 4" folder [Documents > Electronic Arts > The Sims 4] to your desktop (save it for reference) and delete the localthumbcache.package file in your “The Sims 4” folder. Then check in a new game save to see if this issue is still occurring. If the issue is gone, please re-add the Mods/CC one at a time until you find the one causing the issue. If you have a lot of Mods/CC you can try the 50/50 Method.