This is what happens when chemistry nerds try to flirt! The pH scale runs from 0-14, with 7 being neutral, below 7 acidic, and above 7 basic. So calling someone "a 10" on the pH scale is technically saying they're basic (alkaline) - which in slang means boring and mainstream. It's the scientific equivalent of saying "you're hot, but your personality is like room-temperature oat milk." The perfect chemistry burn that would make Mendeleev slow-clap in approval.