A person who likes their guitars (and everyone else's for that matter) tuned to standard E (Low to high E A D g b e). These people, who despite the name may be of any age, dislike the practice of tuning a guitar or bass to alternate tunings such as dropped D (D A D g b e) and show great disdain for those who do because...
Well, who knows.
These people could be the biggest Thin Lizzy fans in the world but wouldn't tune down just a half-step to E flat to play one of their songs correctly. They will often moan on about how it's not necessary to tune a guitar out of E but, when prompted for a reason why, they will just mutter, trail off and then be quiet again.
Standard Grandad: Oh, I see you're a Led Zeppelin fan, so am I! Favourite band since I saw em in '72, got all the LPs! how's about we jam on Moby Dick?
Drummer: Sure thing. But, uh, you'll have to tune your guitar to drop D, that's how Jimmy Page played it.
Standard Grandad: ...Forget it, I can't stand Led Zeppelin, bloody fiddling about with tunings *throws guitar in trash*