One way is, “I’d like to talk to you about something serious. When would be a good time for you?” That gives the other person some agency and time to prepare for an intense conversation. It could also be worth discussing or getting some ideas yourself for a safe or potentially peaceful setting. In some instances a coffee shop or walk could be best or a car ride, but in others, maybe a room in the house would be best. If you think the conversation might get explosive, you’d probably want to give yourself an escape plan by leaving a metaphorical or even actual door open. And if the time is past but the talk still needs to happen, no using regretting but just do your best planning it now. A book came out a few years ago called Difficult Conversations that I thought was very useful. You might want to look for it.