Q: How do porcupines have sex?
A: Very, very carefully. — mE123

While true, porcupine sex is far more entertaining and, uhm, educational:

"With his pointed penis fully unsheathed and erect, [the male] rears up on his hind legs and, from a distance of about six feet, begins to squirt her with urine — an amazing feat, since most male animals cannot urinate with an erection. She does not like the scent bath and growls, snarls, and snaps at him until he stops.

"He often approaches her on only three paws, using one paw to hold his penis and gently stroke it. Before the male mounts the female from behind, she obligingly folds down the quills around her read end. Otherwise mating would be impossible. When they make contact — and only if all of her rear-end quills are down — he thrusts his penis into her. This is the most dangerous time since young, inexperienced females don't always lower all their quills fully or move their barbed tail out of the way."

Sexy Origins and Intimate Things (pg 113) by Charles Panati

This system is fairly clever from the female porcupine’s perspective since she gets to fully control with whom she mates. On the other hand, it's very dangerous for the excited male. Still, some animals have all the fun.