Human contact is a very basic need, right after air/water/food/shelter, and it's an almost physical pain, akin to starving person/resturant window, to watch casual affectionate touch when you're a physically-oriented person and you're not getting enough touch. Having friends willing to give you hugs long enough so that you can relax and just let yourself hug and be hugged is the only cure short of a relationship that I know of.
Brief hugs feel the worst. I've read that when you're starving, after a while, the body starts to ignore the hunger, but if you keep getting little bits, the hunger stays, sharper than ever. A brief social hug is just long enough to know that you want to be touched, you need to be touched, but you don't know if the other person is willing to let you stay holding on for as long as you need, and it's greedy and selfish and pushy to try and stay for longer than they're comfortable with. It's worse to ask for it, because everyone knows that if you ask for something, your friends will accomodate you out of pity or because they feel obliged to, not because they really want to hug you. It's worst of all when someone you neither like nor trust who's still in your social circle offers to hug you. You can't hug them back, properly, because you know if you allow anyone to hug you, you may break down in tears, you don't want to cry on them, and you're still self-protective enough to want nothing personal to do with them.
So you flinch whenever you're touched, and shy away from hugs, while meanwhile you're just getting smaller and smaller and ever more desperate inside...