Even if they were 90 percent wrong, your 10 percent is still yours to own.

Proportion of blame is a separate question from responsibility for your own part. When someone has clearly done most of the damage, your share can look too small to mention, and it is the only piece you have any power over. Owning it is not a concession that they were right.

Name your part out loud, once, without requiring them to match it. Keep it specific and do not attach a list of their offenses to the end. It often changes the whole temperature of the thing, and if it does not, you have still settled the piece that was yours.