Finding a reason to echo someone's own opinion back at them after a suitable time where they've forgotten they voiced it is a very effective test for disagreeableness, I've found. You don't need to chase them down about the contradiction. Just note it and take appropriate future actions.
It can even be a bit amusing, if they are insulting about it, to watch them vigorous call themselves stupid for expressing their previous opinions.
It can even be a bit amusing, if they are insulting about it, to watch them vigorous call themselves stupid for expressing their previous opinions.