Rings are a foreign concepts in the wizarding world. So when Draco Malfoy and his fellow Slytherins begin to notice people wearing metal bands on their fingers, they get curious.
DISCLAIMER: I do not own Harry Potter or anything else created by J.K. Rowling.
Also: Fred, Remus, Tonks, and all our other beloved characters survived. Including Dumbledore.
The first time any of the eighth year Slytherins dared to ask about the metal bands was in DADA, when Pansy Parkinson raised her hand before class began and asked Professor Lupin what was on his finger.
The werewolf had laughed and proceeded to explain what a wedding run was. Needless to say, the class didn't get much work done that day.
The second time was in Charms, when Blaise Zabini noticed the ring on Professor Flitwick's finger and asked him if he was married.
Flitwick had said no, it was an engagement ring, and that was the end of that.
The third time was when Theodore Nott noticed the ring on Ginny Weasley's finger at lunch and asked her what that was all about. The redhead had smirked and said it was promise ring. when further questioned, she explained that while neither she nor Harry were ready to be engaged, they wanted something to symbolize their relationship and devotion to one another.
The fourth time was when Draco Malfoy stopped Hermione Granger in the hall after Potions to ask her about her ring. She had told him it was a purity ring, and, after spending a good half hour explaining what it was to him and the rest of the Slytherins, found herself being thoroughly snogged by Draco, who seemed quite... supportive of his girlfriend's decision, surprisingly.
The fifth time was when Millicent Bulstrode asked Luna Lovegood about her ring when entering the Transfiguration classroom, only to be told that it was to keep away Towries. Just what Towries were, no one knew.
The sixth time was when Daphne Greengrass asked Adrien Pucey's Muggle girlfriend what her ring was for when she bumped into them in Hogsmeade. She was told that it wasn't for anything in particular, she just wanted to wear a ring today.
The seventh, and last time was at Graduation, when Professor Dumbledore announced that they would be handing out rings. Tracey Davis' s inquiry as to what rings the Professor was talking about was answered by Susan Bones, who informed her that it was a graduation ring.
The eighth year Slytherins thought they knew quite a lot about rings after that.
Until, of course, one of them decided to get married and their spouse wanted to do the muggle way, rings and all.