In my case in was way back in 1985 or 1986 during or shortly after high school with my younger brother a mixed group of friend play a AD&D 1ST EDiton game (about 10 of us) in one of the classic modules.
A buddy of ours, Ralph (who due to his parachute pants & funky boot was always an elven fighter or ranger with elven boots & elven cloak, Ralph wasn't very bright or swift on the uptake, not stupid just lacking common sense GOD gave a chipmunk. He never did understand why he got arrested for trying to marry a 15 year old when he was 23. DOH!), got lucky after one combat and got a vorpal blade long sword. Mage ID-ing it explain he should never use it against undead. To which Ralph the HORROR Film fan extrodinaire honestly replied, "Um what's an undead?"
Everyone eyes open wide as Yuri and my Brother Keith both exclaimed, "You can't be serious? Are you?"
Ralph, "Yes, what are undead?"
Keith, "Um, Pat should we tell me or will you?"
I peered up from behind my DM yellow DM screen from reading a magic item description to the party's mage, swiviled my head backa forth like a Terminator scanning targets, locked in on Ralph, and began to smile very wide and evilly. LIke a Red Dragon who just had his combo meal of dinner and loot delivered to his lair and shook my "NO!", "Let him learn he should know that already."
ALL the while Yuri was exclaiming; "OH CRAP! Pat's smiling. The DM is SMILING! DAMN IT all to *(*%(% Ralph, you made the DM happy, never made them happy unless it with a pizza, a hot chick they like, new dice, or all of the above. We are so in trouble!"
Jeff H, "Dang it! WE are going to die. He is already rollign dice."
Next encouter out of town was with a LARGE mixed group of skeletons and zombies. Elvis Ral alph(Ralph the elven super ranger w/ vorpal blade in hand) charges.
DM: You have initiative vs. zombies.
Ralph: "OK. I roll a 20, a natural 20. with my 18/00 strength and now double damage and looky and Rolled max damage. 1d8+6(str)+3(V blade enchantment so that's 17 times 2 is 34 points. CRUNCH! right?"
Party in background: "GROAN! Here is comes!"
DM(with a straight face follow by a grin and evil laughter):
"Zombie is not injured but you take 68 points of damage! Your body looks like burnt BBQ! You scream like a little school girl."
Ralph: "WHAT? HOW? I only have 54 HP! That would mean that I am...."
Group: "DEAD!"
DM: "You just learned the hard way what undead are. Maybe night next you won't flip off the cleric! {evil laughter}"
Ralph: "As I go down, I yell CLERIC! 150 gp to heal me ASAP!"
Yuri: "Hehe, and he laughed at me for buying potions of healing instead of a really big mace!"
Ralph spent the next 5 hours hiding behind the magic user and cleric every time they ran into skeletons & zombies but the stupid fool charged the first vampire they ran into and nearly bit it again! It took 10 minutes for em to stop laughing and get my fat butt picked up off the floor. he last words to the cleric were; "Don't worry it's not an undead like skeletons and zombies, right!???" Cleric: "Um, well, uh, actually it kind of (ZAP! as Ralph score another near perfect hit) is, oh nevermind. Let's see do I have another cure moderate or serious wounds left?"