Taking aside a person's preference over Justin or Zayn (I, myself, would go with Zayn every time) it is important to consider the health repercussions of licking another person's body part.
The foot is awash with potential bacterial infections. Tinea pedis, or athlete's foot, is one of the more well known fungal foot conditions. It got it's name because because of the tendency to infect athletes who often wear hot, sweaty shoes that provide a breeding ground for this fungus.
(Athletes, or... Teenage pop stars who also wear trainers, and spend an awful lot of time under hot studio lights or dancing on stage, maybe?)
This is just one of many possible revolting conditions to trouble the feet. I haven't even spoken about ingrowing toenails, blisters, corns, bunions... There's a whole world of possible pain down there.
And the less said about the other alternative, the better...
In short, I'd go for option c) neither.
