"Have a cigar, old chap." This dialogue could mean a lot of things in the right context. A lot can be packed into a simple line subliminally. It's called SUBTEXT, and darned hard to pull off. Throwing a few lines together to get a point across is propaganda, and not interesting to read.
I'm working on micro tension in my dialogue. Here are a few thoughts on How to Write Subtext in Dialogue.
1. Use dialogue that brings out Hidden Agendas and motives.
Most conversation has under-the-surface tension from the past shared history of the characters. Who is calling the shots? How do they lead the discussion?
2. Show how the characters really feel about each other
Jane Austen writes characters who are forced to endure the company of others they
would rather avoid. She specializes in pent-up emotions.
3. Your characters must REACT to information they hear. Whether it's infidelity, or simply that someone will be later for dinner, have them react to it. A scene will ring hollow if they don't.