How to roleplay a villain conversations with other villains... with the party listening in.

So, the title kinda explains what I'm asking. My next session, I have a pretty big and important scene coming up where (if they hid and listen, and knowing them, they will) they'll watch two villians finally meet, where the worst one explains some major plot points, which the players will over hear. Its not the first time they done this but last time I struggled to have a conversation with myself as I was just rambling and not really following a script and that conversation ended because I ran out explaining things and just wanted them to interrupt the villain.

This time though, I want do it properly as I know its coming this time. So would you say that I should write the entire scene out, the conversation and the plot points that are dropped? Or should I just ramble again? I feel like my players would know if I'm reading something aloud, rather than acting it out....

any suggestions?