I freeze up sometimes when my flatmate says to me "Hey I'd like to talk to you about something" and then waits a few seconds before bringing up something totall

I freeze up sometimes when my flatmate says to me "Hey I'd like to talk to you about something" and then waits a few seconds before bringing up something totally everyday thing that's not a complaint, while I've already flicked through my mental rolodex of possible co-living infractions several times for candidate complaints.