I still remember one of my buddies, who does laugh a lot, saying at one point in a conversation "Man, I haven't laughed in a while" and starts looking anxious. I obviously laughed at this, and he laughed back, and I realized that he did indeed laugh at almost everything. And I loved that about him.
From that point on, I've tried to laugh as much as possible.
Janitor is sweeping - deep belly laugh
Light flickered - hilarious
Out of coffee? - You would think he is front row at a stand up routine.
Not this much, but I did laugh at the thought of someone laughing at things like this.