From the Prank vs Prank couple. Details on this prank from the YouTube description:
I found a hair extension at the mall that matched my girlfriend’s hair perfectly. I brought it home and waited until she was preoccupied, so I could pretend to cut her hair. We had plans to go to the movies that night. She was looking up what movie we should see, and while her back was turned to me, I held the hair extension up to her hair and grabbed onto her own hair while making the scissors make a snip sound. She turned around while I still had the hair extension in my hand and she instantly freaked out thinking that I cut a chunk out of her hair! I think this was the first time she actually had tears in her eye when I pranked her. She was so upset and mad at the same time, until I she realized that it was not really her hair and I didn’t cut anything or ruin her hair. Shout out to Alli Speed from CTFxC for the idea.