Not so much the worst (someone got me a Bugs Bunny tie once - and I've only worn a suit like a dozen times in my whole life), but the worst opening experience for sure.
When I was around 10-ish, my church asked all the parents to send along gifts to a near 25th whatever it's called, churching, so the childrens group could open presents and be all Santa Jebus yay! My folks, not wanting to do the right thing, just grabbed some packages sent by my Grandmother from under the tree, small, feeling like clothes, and sent that along - the plan, I found out later, was to not have us open anything too good at church, and save that for Xmas morning. Cut to church, my little sister, about 6-7 at the time opens her present, mind you, in front of every kid I knew at the time. Yippy dippy, it's a package of My Little Pony underwear.
The fear set in. My package was the same size, weight, and from the same person. I knew, as I saw all the other kids in our group opening toys and games and coloring books, I was doomed. I stepped to the side of the room, and opened it secretly, just tearing the corner or so open to get a glance. GI Joe or Star Wars underwear. Oh man. That did something horrible to me. I had to lie and deflect when everyone asked me what I got. And when my parents picked us up later, and found out, they were deservedly embarrassed. My sister loved her gift, and maybe had I opened mine in the privacy of my own home, I might have liked mine too.
They made up for it by taking me to Toys R Us the next day and buying me a GI Joe figure, which was nice a couple days before Xmas. But that day taught me a pretty fun lesson about shame, and cheapness.
The end.