F&@! you, too
I was going for a rainy day shot of an approaching BART train. It wasn't until I downloaded the photo onto my computer that I realized the guy walking away from me on the platform was flicking me off. Maybe it makes me a total child, but I think that is completely hilarious.
Note: There has been some doubt raised on whether this is a legitimate instance of The Finger or not. I invite you to go here: www.flickr.com/photos/inadvertentgardener/3310242595/size... Scroll around, and judge for yourself.