Two years ago, when I got married, my buddies and I wanted to end the wedding in style with a surprise for everyone else.  Our wedding took place in my wife's Lutheran church.

My buddies and I like to go boating, so I had them wait until the vows were over and then had them throw orange smoke canisters (used for signaling emergencies on boats) and glow sticks down the aisle.  The church was not very big, so the smoke permeated the place a lot more than we thought it would.  Setting those things off outdoors on my boat in preparation didn't really give us a good idea of how much smoke they really put out.

People started screaming even though I was shouting that it's all right and just emergency smoke grenades.  My wife's father grabbed her and led her out.  When I got outside, I saw that she was kind of disoriented.  Soon, she was yelling at me, along with her side of the family (jerks).  We ended up having to pay for the damages for the church, which was a lot.  Also, the next Sunday's service had to be held in the fellowship hall due to the damage.

My buddies and I still joke about it, but my wife is still VERY sensitive about it.