Many Warcrimes. So many. But as for the worst I've done, that's pretty easy.

Sex trafficking. My band of rogue Russian Soldiers made their money off the trading of human flesh. Different species like the Kurin, Nyaron, and Rabbies were especially prized, particularly the Moyo, I always sold them last, since they could make my colony passive income by harvesting their blood, which could be used in the production of Blue Meth, while we waited for the next band of Slavers. There was also very few mental breaks, from the Colonists at least, due to the constant buffs from doing unmentionable crimes.

That colony suffered a very deserved downfall that began with a mimic killing the only dedicated cook.