Quick answer: Everyone reaches for the floor; the last player to touch it drinks.
What Does 4 Mean in King's Cup?
Four means “floor.” As soon as the card is revealed, players safely touch the floor or the agreed surface. The slowest player takes the action.
Common 4 House Rule
For accessibility, choose the tabletop, raise four fingers, or tap a visible object instead.
House rules differ by group. Confirm the meaning before the first card is drawn, allow anyone to choose a non-alcoholic alternative, and never pressure a player to participate.