My grandfather is 85 and still doesn't need glasses.

This joke plays a delightful trick on our expectations, using a classic misdirection (Review) technique. When you hear about an 85-year-old who "doesn't need glasses," your mind immediately jumps to their vision. We all know that as people age, their eyesight often deteriorates, making corrective lenses a common necessity. The setup makes us imagine a remarkably spry and sharp-eyed senior, perhaps blessed with incredible genes.

But then comes the punchline, which brilliantly redefines the word "glasses." Instead of referring to spectacles for seeing, it suddenly means drinking glasses, the kind you pour a beverage into. The humor comes from this sudden, literal reinterpretation of the phrase. It’s a wonderful piece of wordplay that takes a seemingly impressive health boast and twists it into a humorous, slightly irreverent observation about someone's drinking habits.

The comedic genius lies in swapping a positive health attribute for a completely different, and perhaps less dignified, reason for not needing an item. It's an unexpected reveal that makes us chuckle at the clever linguistic flip and the image of a grandfather happily bypassing the glassware.