By my definition, a defense is unconscious. So if you were purposely trying to make her laugh, you were not using laughter as a defense. I would ask, what was your unconscious intention? It strikes me more that you were being false with her, intentionally acting a role. Then you became angry that she didnt see through this role-playing to the real you, ie "blaming her for laughing too much." But you set her up in a no-win situation. But so did your mom.

I think thats why my ts usually refuse to laugh in my sessions, unless THEY make a true joke or witticism.

But it also explains why it was only ever safe to try to make my own mother laugh, but i think it hid my same anger at my no win situation.

Complicated! But a breakthru for me, i think!