Hmmm, I personally think screaming is the weakest (and most annoying) thing. But other ways are funny. One time I went with 2 of my friends, and we were in the Haunted Mansion. At the part where the streching room gets completly dark, someone yelled "don't touch me there, stop!" that was great! I was actaully recording at the time. My friends were making noises on the ride also.
Around the same time, laser pointers were famous, and we were on the TTA. My friend and I turned them on during the Space Mountain part where you go through the queue, and made them point all over the people in line. After we got off the TTA, they told us not to use laser pointers anymore.
This was back when the Skyway was still open, and we went on the TTA like 10 times. That was a great day.
I probably wouldn't do anything like this again, and when I hear people screaming, they look like idiots to me. If your gonna do a joke, make it original, and don't make it so it ruins someones day.