When I was about 12, mom and I were in church for Good Friday, the most solemn day of the church year.
On Holy Thursday, the host was moved from the main altar to a side altar that is supposed to represent the tomb. The lillies decorating this side altar were absurdly tall. Both mom and I thought they were hilarious. We were so close to laughing that we couldn't even look at each other. Finally, I had to get up and leave.
Another thing that almost always make me crack up is the announcement of some subway trains. At each stop a voice announces, 'This is X stop. Next stop, Y Street. Watch the closing doors, please'. The problem is that the last is said in a particularly silly way. I'm far from the only one who laughs.