Years ago I lived at the Grand Canyon, AZ. My roommate and his girlfriend both came up with a great gift idea for the other: binoculars. They also wanted me to go with each of them (separately) to Flagstaff to find said binocs.
In two consecutive days, I trekked the 80 miles down to a Flagstaff outdoors shop with both of these people, and the guy behind the counter recognized me on day two, with a little, "What are you trying to pull?" expression on his face.
I frantically made "DO NOT ASK!" gestures behind my friends, and they ended up each buying the exact same make and model.
Christmas morning, they opened their gifts and called me various names for letting them do this to each other.