The first prank Data decided to try out was the wedgie. This particular prank mystified him the most. Why would pulling someone's underwear up be funny?
He was still pondering this when Wesley entered his quarters. "What did you want me for, Data?" he asked.
"I wished to try an experiment, Wesley. Are you willing to take part in it?"
"Yeah, sure," the young Crusher said uneasily. "What are you going to do?"
Data knew that Wesley had to be unaware for this to work, so the android didn't answer Wesley's question. "Turn around so that your back is facing me."
Wesley did as Data asked, and the android swiftly lifted the boy's underwear and pulled. He pulled so hard that Wesley's underwear ripped. I don't think that was supposed to happen, Data thought.
Wesley swore like a sailor and keeled over. "What the heck, Data?!?" he exclaimed through gritted teeth. "What did you think you were doing?"
"I was merely attempting something called a prank. It is intended to be funny."
The son of Dr. Crusher was angry now. "Well, that's not funny at all. My mom is going to hear about this." He grabbed the piece of cloth that Data had ripped and stormed out of the android's quarters.
Needless to say, Dr. Crusher did not speak to Data for two weeks. But obviously everyone else thought that the prank was hilarious. Even Geordi mentioned it to Data, saying that it was "a good one."
The android still didn't understand how a wedgie could be funny, but a few days later, he began plans for his next prank.