Mount & Blade II: Bannerlord

This is actually pretty easy to get. I had over 30 nobles and vassals already in my prison from being at war with Vlandia, but if you don’t then just find the corresponding owner of a castle or town and capture them or a clan member. In my case I had Belgir, owner of Verescand Castle. I went up to the castle and besieged it which is a -5 relations loss with their entire clan, then cancel the siege immediately and repeat until you’re at -100. Finally, execute your prisoner :-) Any member of the clan “should” work as they will all have -100, but to be safe make sure they are classified as a lord, or the actual owner.

Or you can just start executing all your prisoners which in turn will plummet your relations with almost everyone, and pretty soon the next head ready for the axe will have -100 relations.