Collect all four pieces of the knight armor to reduce damage taken to
half. However, if you lose 50% health, the armor will break and you will
take normal damage in your underwear. The armor pieces can be collected
as follows:

Beard: In the rear of the "Wave Of Style" hairdresser's shop in
Royal Flush Plaza.
Knight's Armor: Successfully complete the game with an "S" rank.
Knight's Boots: Purchase for $2 million from "Moe's Migitations"
on the Platinum Strip.
Knight's Helmet: Rescue Jack in the "Meet The Family" mission, and
defeat him in a game of poker in the "Ante Up" case.