Check for collision with player

    if (
        player_x < enemy[0] < player_x + player_size
        and player_y < enemy[1] < player_y + player_size
    ):
        pygame.quit()
        sys.exit()

    # Remove enemies that go off-screen
    if enemy[1] > HEIGHT:
        enemies.remove(enemy)

Life would be so much simpler if it was possible to kill off your bad emotions this way.