My friends and I wanted to do shit like this; at my university, there were night classes being taught in these huge-ass lecture halls with large windows. We wanted to coordinate it so that one of us would've been in class in the back of the room, then all of a sudden a spotlight comes on with the Bat signal. The friend would stand up look around, then run out of the lecture hall. Then 5 minutes later, he'd run in half dressed up, grab his bookbag that he forgot, and run back out.
We got as far as finding a huge-ass spotlight and reserving a bat-suit at a costume place, but my other friend was lazy as hell and didn't finish making the "bat" silhouette that needed to go over the spotlight.