A reminder on how For You works: it finds people who liked the same posts as you, and shows you what else they’ve liked recently.
It uses co-liked posts to connect you to other people.
When you use "Show less like this", For You penalizes people who liked that by cancelling some of the co-likes.
When you press "show less like this" we make likes of people who liked that post have less importance for you.
Specifically, we disregard one like that you have in common with them.
As a result you would see less content from them.