QUESTION: Why do people kiss under mistletoe?

ANSWER: It’s enough to get you running in the opposite direction at the office Christmas party – so what’s the cause of our annual puckering grief? Mistletoe is traditionally associated with fertility, with some even considering it an aphrodisiac. The tradition of kissing, however, is said to date back to Norse mythology when Baldur (god of truth and light) was killed by an arrow made of mistletoe. His mother was so distraught that she wet tears of white berries which brought Baldur back to life. The legend goes that she was so overjoyed she blessed the plant and promised a kiss to anyone who passed under it.

source: marieclaire.co.uk/life/christmas-traditions-answered