Disclaimer: Harry Potter is owned by an author I currently want to hit over the head with a large, blunt, heavy object. But that's not stopping me from writing L/J stories...
James Potter wasn't after Lily Evans because of a dare. Yes, he had been dared to ask her out, but that's not why he was rapidly gaining a new respect for the girl.
She had turned his down. And, thus, he was obsessed.
She had openly insulted him. And, thus, he had a feeling that he was in love with her.
Not that she'd ever share a feeling even close to his. But at least he had long since given up asking her out and tormenting people in public. No, he was a 'mature' 7th Year, and above those childish tendencies. Or that's what he tried to tell her, before she hexed him.
It took a whole month to get Remus to tell him the counter-spell. And he was forced to buy him a year's supply of chocolate.
James soon learned that talking to Lily wasn't the smartest thing in the world to do, so he did the next 'best' thing- stalking her.
People began to wonder why Lily Evans started to look paranoid.
Lily Evans wondered why she'd hear heavy breathing behind her on her patrols of the school. She also wondered why Potter was never around, but she figured he was probably plotting something devious with his fellow conspirators.
One day, Sirius had a brilliant idea: leave presents for Lily where she'd find them! Remus promptly stuffed a sock in his mouth, and Peter stole some of Remus's chocolate, but James thought it was an excellent idea.
Lily Evans became increasingly paranoid. Her friends told Sirius that she'd come in from her patrols muttering about loud breathing and flowers everywhere. Within a week she'd found so many lilies in the halls that she was sick of them. Sirius informed James. Lily started finding roses everywhere. Dumbledore wondered vaguely if the Head-Girl needed a visit to a Mental Home, or at least St. Mungo's.
Peter suggested candy, as he snitched the remainder of Remus's. Lily Evans suddenly went on a candy-free diet, and complained of dreams where she'd be stalked by Liver-flavored beans. Remus suggested that James stop making the poor girl paranoid, and buy him more chocolate. He simply didn't understand how a year's supply of it vanished in two weeks!
James decided his friends were useless. He asked Snape for a suggestion. He was, of course, rewarded with a very nasty curse that made him talk in a very high-pitched voice for the following week. Lily momentarily forgot about her stalker, due to laughing at James.
It took a few more months, but James finally figured out that stalking was not the way to win Miss Evans's heart. He asked her very politely if she'd mind if he went with her on Nightly Patrols. She agreed instantly, glancing over her shoulder nervously.
He had to admit that he had behaved very nicely. He had asked her about her family, found out that she didn't used to be paranoid, and only ruffled his hair once. She even asked him to go with her the next night. Apparently she was afraid that someone was going to attack her.
Now where on earth would she get that idea?