I'm going to tell my bil that he's a lowlife who doesn't deserve an opinion
Why do you think so low of your brother in law?
He hated my answer to his opinion
It's not very nice to call your family a lowlife. You probably hurt his feelings.
In his opinion, I'm a dick.
Your brother in law must feel very passionate about their stance and your opinion felt offensive. If you know how much they care about something, let them relish in it and try not to be so critical of their preferences.